Sokolov Painting 7-1
In the first area you enter, before going to the Refinery, you can find this painting in a building on the third story. Blink up to the balcony of the building and enter to find the painting in the corner in front of a Weeper.
Sokolov Painting 7-2
Once you have dealt with Daud and gotten his key, you will need to return to the beginning of his hideout to unlock the set of double doors to the right of the window where you entered. When you do, there will be a chain in the center of the room that leads downwards. Follow the chain halfway down to a landing and the painting will be there.
Sokolov Painting 7-3
Once you find Granny Rags and Slackjaw in the sewers, go up the stairs on either side of the room and you will find the painting, “The Outsider and the Circumscribed Void” in the small room there.