Adept 34501 is a Woman In Black you find in the Knights Templar cathedral. Facing the entrance to the basement (the room has a pillar, a keypad, a guard, a camera, and a turret), turn around, and go up the stairs. Turn right at the first landing, and you'll find a room with a WIB in it. Knock her out to get the achievement.
An easy way to do this is to puff her with the pepper spray, then hit her with the electric prod.
The meaning of the name of the achievement is explained if you read the books in the room, particularly the one about her observations of Gunther.