Max Ernst. Solitary and Conjugal Trees. 1940.
This is the third of the 10 collectibles. Remember to pick it up using , regardless of whether you already have something in your inventory. It looks like the moon (see the trophy tile).
At the very beginning of Chapter 2, as soon as you enter, you'll see the moon at the top right of your screen. You need to drag the rock back and jump on it in order to jump up and reach the moon. See the video (0:30) for precise location: