Near the end of the mission, you need to go into the hidden room in the basement. Access this from the door on the ground floor of the estate, or via the kennels. You will come across a statue / bust. Press the eye to open secret door. Inside the secret chamber you will find The Isometry of High Overseer Thaddeus Campbell

Inside the Art Dealer's building in the Distillery District. Look for a self portrait of Sokolov: Light along the Inverse Curve.

Go to the Art Dealer's building use the key (or blink your way to the upper floor's door if you don't have it). If you want the key - get it from the civilian woman you save from thugs by the stairs, lower alley in Distillery District.

That safe on the third floor of the Art Dealer's building which the thugs are trying to get into... open it. The Combination is 879. Inside is Custis, Morgan, and the Postulate Child

Inside the Art Dealer's building go up to the third floor. You will find some guards at a safe door. Across from them is a room where you will find Daud and the Parabola of Lost Seasons

Near the end of this mission you will find The Obtuse Argument of Lady Boyle in the middle of the first floor of Sokolov's house.

It's easy to spot, out in the open on the main area.

Find Lady Boyle's bedroom. Either get past the guard by the stairs leading down to the kitchens, or by using the balcony to get in, you will find The Spymaster's Axis of Asymmetry on the upstairs of the Boyle Mansion, in the large bedroom.

Note: This will appear in one of the three bedrooms on the upper floor. The video may not be the same for your play through.

Still inside Boyle Mansion, on the same floor as the last painting, find the gallery room (large room in the middle-ish). In the middle of the room will be Vera Moray and the Affix of Her Skin

Inside the music room with a large piano, which can be found on the second floor. Look at the roof over the fireplace, it's hanging there. The Empress and the Empty Set.

Jumping from one roof to the balcony / pipe using blink, you'll find this painting on the third floor of the building in waterfront region (before heading off to the refinery). The Commutative Rats and the Weeper.

After you have passed Daud and got the key from him, return to the start of his hideout. The key unlocks a set of doors to the right of where you entered. Follow the chain you find. Half way down you will find the painting. The Torturer's Quaternionic Groon.

When you're down in the sewers and come across Granny Rags and Slackjaw - take the stairs leading to a small room with the painting. The Outsider and the Circumscribed Void