The Art Connoisseur is a contract in Mission 3 of Dishonored Death of the Outsider.
The Art Connoisseur Walkthrough
This contract is so easy, I actually got it by accident. Right next to the skiff near Dead Man’s Bluff, a new barge will appear during Mission 3. There is a locked cargo area on the barge that contains one of the paintings you need for the Art Aficionado trophy. Luckily the key is so close by, its almost ridiculous. Dive in the water, look under the barge and you will see a corpse floating underneath it. Loot the corpse to get the key, open the door to the cargo area and grab the painting to complete the contract.
All Mission 3 Contracts:
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Yeah the corpse under the boat never appeared to me in OG+, soooooooo……
It might be in a slightly different position but it’s definitely there in the water. Dive deeper or look behind the boat. It’s in there somewhere.
It spawned for me in OG+.
Walkthrough Spoiler on this… After trying to find this a few times using Foresight to dive down, I tried just diving down and almost drowned twice. The water here is DEEP! I went back to searching with Foresight and realized the body is immediately under the boat, as in floating up against the bottom of it as though he was just ran over by it. If you bring your skiff, drop into the water between the two boats and just dunk your head under the surface a little. Easiest way to get the key is by using using Foresight to mark the key so you can see it when you go into the water to grab it.
For me the corpse was on the inside of the barge slightly clipped into the floor (probably glitched through the bottom of the boat from the water). You can use foresight to go through the bars on the side of the boat and place a displace marker to get inside without the key.