Sokolov Paintings are exactly as they sound, paintings done by Anton Sokolov. They are hidden throughout the missions and total eleven, with each one giving you 300 coins when you grab it. Collecting every single painting will get you the Art Dealer achievement/trophy .
High Overseer Campbell
There’s only one painting in this mission, which is located in the secret room that you might come across in a no-kill playthrough. In the Office of the High Overseer area, you can find a door that leads to the basement, where you’ll find a discolored wall. Next to this wall is a button you can push to open a secret door, leading to the secret room and the painting.
House of Pleasure
All three paintings can be found in the Art Dealer’s Apartment. While the second floor door is unlocked, the third floor one requires a key, which you can get from a woman in an alley that leads to the third area of the Distillery District. Help her out or let her be killed, then you can get the key.
1) This painting is located behind the safe on the third floor. You need the combination to the safe, which can be acquired from the Art Dealer, as part of the second side mission for Slackjaw. Note that the combination is random and changes every playthrough.
2) Enter the third floor door and look to your left to find a door, which leads to a room with the painting.
3) When you go to the second of the apartment, you’ll find two guys looking at the painting. Wait until they move away from it or take them both out, then grab the painting.
The Royal Physician
The painting in this mission is located on the bottom floor of Sokolov’s house, right in the middle of it. There will be a lot of enemies on the bottom floor, so you’ll need to be extra careful if you’re doing a no-kill Ghost playthrough.
Lady Boyles Last Party
Both paintings in this mission are located in the upstairs area of the Boyle Estate. Once inside of the mansion, there is a doorway to the side with stairs going both up and down. A guard is blocking the way up, so wait until he moves to slip past him.
1) This painting can be found in one of the three bedrooms that belong to each of the Boyle sisters and its location changes on each playthrough. You can tell which rooms are the bedrooms, due to their ornate doors. In two of them, the painting will be above the fireplace, while it’s just inside the door to the right in Waverly’s room.
2) In between all of the rooms is a big room with a lot of glass cases. The painting is in the middle of this room.
Return to the Tower
This painting is located inside of the tower, in a room that’s adjacent to the Lord Regent’s bedroom. When you are in the tower’s foyer, there will be a balcony overlooking the room. This balcony leads into the bedroom mentioned, so Blink up to it and you will see a fireplace. This fireplace leads into the room with the painting, so you can crawl through it. The painting is above the fireplace in this room.
The Flooded District
There’s three paintings in this mission, with the last one actually being missable. That painting is located in an area only accessible if you do all of the side missions for both Granny Rags and Slackjaw.
9) When you get to the bridge from the chain you climb up in the beginning, face towards the Daud’s base marker and look to your left to see a balcony. Get onto the rooftop, then onto the higher one and drop down and get onto the balcony. The Sokolov Painting is inside.
10) This painting is inside of Daud’s base. After collecting his key, you will need to unlock a door that leads to a chain that goes all the down to the ground, leading to a door that goes to the next area. Instead of climbing all the way down, jump off the level above, where you’ll find the painting.
11) In the area where you find Granny Rags and Slackjaw, go up the stairs and into Granny Rags’ bedroom. The painting is hanging over the bed.