In Thief Basso Job: A Lady's Request side mission, you are tasked to steal Lady Christina's testament
Thief: side mission- A lady's Bequest Walkthrough
You need to go through the doctors office and through the window in order to get to this mission. Go to the marked area and then head down to the basement.
Crawl through the opening on the wall to get to the next area. Loot the place and then drop to the next room.
Grab the painting on the wall The Insatiabe Appetite and head back toward the quest location.
Locate a shelf you can climb and behind a the table barricade you can find the quest item inside the drawer.