Note: this quest will fail if not completed before finishing Open Sesame!.
To obtain this, after entering the Borsodi Brothers' Auction House with Vimme Vivaldi, talk to the art connoisseur, Yaromir Ivanovitz Zaytsev, near the paintings. He'll be dismissive, but tell him you know art and he'll ask you to pick out the one by artist E. van der Knoob. If you didn't already read over the paintings, the correct one is the merchant.
Impressed, Yaromir will pull you to the side and as a way to apologize gives you some useful information: a van Rogh painting, "Starry Night Over the Pontar", is going on the block and while a largely unknown artist, Marcus T.K. Hodgson is a fierce admirer and will likely pay well for it. Vimme will then approach afterwards, curious to know what he told you. You can lie with no penalties or tell him. Note: If you tell him the truth, you'll have to pay a bit more for it during the auction.
Now, start the auction and it'll be the second object put up. If you didn't tell Vimme about it, you can get it for 20 , otherwise you'll enter a small bidding war with the banker and must then pay 60 to get it. Continue the main quest as normal until you regain free movement to walk around and head to Hierarch Square in Novigrad and talk to Hodgson in his shop. He won't hesitate and will immediately give Geralt the Conserved shaelmaar trophy and 500 as payment.
- Geralt is often taken for a boor. Nothing could be further from the truth: though rough-and-rowdy in outer appearance, inside Geralt harbors a sensitive appreciation of beauty and the arts. It should then come as no surprise he was able to impress the art merchant he met at the auction. The connoisseur tipped Geralt off about a van Rogh painting soon to go on the block. Apparently Marcus Hodgson, a famed Novigrad book dealer, was ready to pay a small fortune for it...
- The merchant's assurances proved reliable: Geralt sold the painting at a considerable profit. The ecstatic book dealer also threw in a rare witcher trophy.
- Sell the van Rogh painting to the Novigrad book merchant, Marcus Hodgson.