How to Start Homestead Woodworker Mission
Talk to Achilles
Speak to Achilles who is inside the manor, wandering around. He will explain that he has found a painting to put over the mantel but the house it was being kept in was in the path of the Great Fire. Head to the marked building in New York. Scale it and get to the platform just below the rooftop where the marker is. Interact with the nearby wall to open it and claim your prize.
Fast Travel back to the Homestead and give it to Achilles to complete the mission.
Connor: "It is beautiful, old man
Achilles: "It is. I've found a painting for the space above the mantel. It's being held in New York. If you get a moment, I'd like you to pick it up for me."
Achilles: "Good - it may not be there as the house where it was stored lay in the path of the great fire. If so, worry not."
Upon retrieving the painting:
Connor: "It would have burned had it not been here."