While inside the Stonecutter’s Court, find the Jeweler's Shop to the left of the guards that are chatting under the light. Enter the shop and knock out the guard to the left of the entrance, then turn to the right. Find the three cabinets below the red drapes and use a lockpick on the center cabinet to get the first mask. Once done, turn around and sneak into the cellar. Avoid the person working at the desk while moving to the rear left corner of the workshop. Interact with the painting and use the secret switch to unlatch it to find a wall safe. Enter the combination "739" to open the safe and collect the other item.