How can I explain what a wizard sees? It isn’t something that lends itself readily to description. Describing something helps to define it, to give it limits, to set guardrails of understanding around it. Wizards have had the Sight since time began, and they still don’t understand how it works, why it does what it does.
The only thing I can say is that I felt as though a veil of thick cloth had been lifted away from me as I opened my eyes again—and not only from my eyes, but from all of my senses.— Dresden
Use of the Sight, sometimes also referred to as the "third eye", allows a wizard to gaze upon the world and see its supernatural side, allowing the perception of things hidden to the normal eye. What has been seen through the use of the Sight will remain a lasting memory forever, and will neither fade nor be forgotten. Because of this, wizards don't use it often, for it could easily drive them insane.
The Sight usually shows concepts physically, e.g. if a loved one had recently died, a person could have wounds similar to those of a sword, as thought by Harry Dresden. When Molly Carpenter forced her friends off drugs, Dresden saw the damage done by her as if a laser scalpel had drilled two holes into the victim's head. 
The Sight can break through illusions and is generally the method used by wizards to pierce veils. The Sight can also be induced in mundane humans. One known example is the drug ThreeEye, which gave the user the Sight, but also severely strained their minds, as it was unable to be turned off until the drug wore off.
When observing someone using their Sight as a spirit, it looks like a "blinding burst of light emitting from between and just above the eyebrows and included a tangible sensation."
In the series
"A Fistful of Warlocks"
In Storm Front, Victor Sells creates a drug called ThreeEye, which gives mortals a temporary use of the Sight. Harry Dresden uses his Sight for the first time to scout and then enter Victor Sells' lake house.
B is for Bigfoot
In "B is for Bigfoot, Harry Dresden opens his Sight after introducing himself to Coach Pete Vogon and it shows him that the coach is not human. The Svartalf also notices that it is being observed under the Sight.
At Bianca St. Claire's ball, Ferrovax tells Dresden that if he were to gaze on the Dragon with his Sight, he would see something that would awe him, humble him and quite possibly destroy his reason. Later, when Dresden, Susan Rodriguez and Michael Carpenter are trying to leave the Ball, Dresden senses someone in their way on the stairs leading out. He opens his Sight and Sees Mavra, a Black Court vampire, through her veil. She says that few can see her when she doesn't wish to be seen.
In Summer Knight, Harry Dresden uses his Sight to see the Stone Table and the landscape surrounding it. He Sees an area seething with conflicting energy. Observing the battlefield, he Sees both Faerie Courts preparing for battle, including both the Summer Queen and Winter Queen, the Sight of which leaves him wracked with pain.
In Blood Rites, when going through the shelter above Mavra's lair, Harry Dresden opens his Sight so that he can See who is a Renfield, and who is a thrall. While his Sight is still open, he Sees Karrin Murphy again as well as Jared Kincaid who appears as a giant, horned, winged demonic man. 
In Dead Beat, Donald Morgan uses his Sight to scan for Veils prior to a meeting. Later, Harry Dresden uses his to remove the veil around Sheila's apartment. He again uses his Sight to scan for veils at the Field Museum of Natural History.
In "Something Borrowed, Harry Dresden uses his Sight to try and find out what is wrong with Georgia Borden. He Sees that there is a few spells working on her, one possibly being a sleeping spell, but due to the distance, he cannot See too precisely.
In Proven Guilty, Harry Dresden uses his Sight to look at the crime scene at SplatterCon!!!. He Sees that Black magic was definitely involved. It's what the Gatekeeper Rashid had put Dresden on the lookout for. Later, Dresden takes a look with his Sight at the Phobophage victims at Mercy Hospital. First he Sees Karrin Murphy in a white angelic tunic with battle stains. Dresden Sees Rosanna Marcella, Molly's friend, with psychic black holes bored into her head, her psyche savagely mauled. Dresden Sees Clark Pell would survive because the monster couldn't get to his psyche. When Dresden looks at Nelson Lenhardt with his Sight at St. Mary's, he finds the same two holes in his temples and deduces that Molly Carpenter forced Rosie and Nelson off drugs to protect their unborn baby.
In White Night, Harry Dresden decides not to use his Sight to examine the body of practitioner as he's "getting sick of doing that". During a flashback to the Ghoul attack on Camp Kaboom, Dresden uses his Sight to locate the Ghouls through Anastasia Luccio's defensive veil.
In Small Favor, Anastasia Luccio describes a new aspect of the Sight. She refers to a sense of precognition that every Wizard develops as they mature. This is in response to Harry Dresden recognizing Demonreach, a place he has not been before. When Dresden asks why this is the first he has heard of it, she replies that experienced wizards do not tell younger ones about the Sight as the result is often very annoying, misplaced prophecy in place of acknowledging hard truths.
In "Day Off", Harry Dresden uses his Sight to find out what is wrong with Kirby and Andi Macklin. It shows him the thick bands of power that are around his apartment and lab as well as a number of psychophagic mites attached to the couple, giving off shimmering energies.
In Turn Coat, Harry Dresden senses that he is being followed during his drive home. He opens his Sight and Sees the Skinwalker, Shagnasty, and the pure evil of the monster nearly disables him and almost sends him insane. Even after he closes his Sight, every time he recalls the attack, he is almost knocked out by the Sight memory. He manages to walk to Billy's by calculating prime numbers in his head and keeping his thoughts off the attack. To recover himself, he goes into a dark, quiet room and little by little, he desensitizes himself from the memory until he can think of the Skinwalker and not fall to his knees. Dresden refers to these sorts of reactions as "Sight trauma".
In Ghost Story, Harry Dresden's ghost uses his Sight at the Office in the Between. When he observes the guard at the elevator, the guard's sidearm morphs into a glowing sword. The guard gently stops Dresden and forces his Sight closed before much more can be observed. The guard apologizes and states that Dresden might have been harmed. The guard's name tag reads "Amitiel".
Later, Molly Carpenter uses her Sight to verify if Dresden's Ghost is truly present. From Dresden's perspective, it appears as if a sudden light appears between and just above her eyebrows. Her Sight not only reveals Dresden's presence, but allows them both to communicate verbally. Apparently, "It encompasses a lot."
Dresden's ghost uses his Sight again to See through Carpenter's illusions when she fights the Fomor servitors. When he realizes the danger she is in, he shuts his Sight away as the concept of Seeing her die (and therefore never being able to "un-see" it) leaves him panicked. The Leanansidhe remarks that Dresden has his mother's Sight.
Dresden and Carpenter both again bring up their Sight for scouting purposes during the assault on the Big Hoods' hideout and during the subsequent battle with Corpsetaker, Dresden has his sight wide-open. Interestingly however, no Soulgaze occurs when he locks eyes with Corpsetaker.
In Cold Days, Harry Dresden recalls his viewing of the Naagloshii under the Sight. Although the memory won’t go away or fade into the past, he claims that he has gotten used to it. The memory causes a brief stutter in his speech.
When talking with Rashid, Dresden notices a hesitation in the Gatekeeper’s speech indicative of stumbling over a Sight-memory. Rashid recommends not making a regular practice of using the Sight to identify Nemesis.
In Skin Game, Karrin Murphy and Harry Dresden find out that there is apparently a creature hiding in the building where they have been meeting with Nicodemus Archleone and his group. Murphy asks Dresden whether he can discover the creature by using his wizard-Sight. Dresden claims that he could – the Sight is the direct perception of magic and can cut through any kind of illusion or glamour or veil, but that the last time he did something similar, he ended up incapacitated for a couple of hours.
Wizards can see things most people can’t. It’s called the Sight, the Third Eye, a lot of other names. If a wizard uses his Sight, he can see the forces of magic themselves at work, spells like braids of neon lights, veils pierced like projections on a screen. A wizard’s Sight shows things as they truly are, and it’s always an unsettling experience, one way or the other. What you see with the Sight stays with you. Good or bad, it’s always just as fresh in your mind as if you’d just seen it.— Dresden
A wizard’s Sight, his ability to perceive the world around him in a vastly broadened spectrum of interacting forces, is a dangerous gift. Whether it’s called spirit vision, or inner sight, or the Third Eye, it lets you perceive things you’d otherwise never be able to interact with. It shows you the world the way it really is, matter all intertwined with a universe of energy, of magic. The Sight can show you beauty that would make angels weep humble tears, and terrors that the Black-Goat-with-a-Thousand-Young wouldn’t dare use for its kids’ bedtime stories.
Whatever you see, the good, the bad, the insanity-inducing—it sticks with you forever. You can’t ever forget it, and time doesn’t blur the memories. It’s yours. Permanently.— Dresden
- Turn Coat, ch. 4
- Storm Front, ch. 24
- Proven Guilty, ch. 16
- Proven Guilty, ch. 11
- Storm Front, ch. 11
- Grave Peril, ch. 35
- Ghost Story, ch. 11
- "A Fistful of Warlocks"
- Storm Front, ch. 24 and 25
- "B is for Bigfoot"
- Grave Peril, ch. 26
- Grave Peril, ch. 28
- Summer Knight, ch. 23
- Blood Rites, ch. 31
- Dead Beat, ch. 30
- Dead Beat, ch. 35
- Dead Beat, ch. 36
- "Something Borrowed"
- Proven Guilty, ch. 17
- Proven Guilty, ch. 32
- Proven Guilty, ch. 33
- White Night, ch 1
- White Night, ch 22
- Small Favor, ch. 46
- "Day Off"
- Turn Coat, ch. 5
- Turn Coat, ch. 44
- Changes, ch. 45
- Ghost Story, ch. 2
- Ghost Story, ch. 11
- Ghost Story, ch. 22
- Ghost Story, ch. 30
- Ghost Story, ch. 41
- Ghost Story, ch. 45
- Cold Days, ch. 15
- Cold Days, ch. 34
- Skin Game, ch. 15