Animal Doctor

This is unlocked by completing the twenty-second mission in the game, which has you continuing to gather evidence on the wolf you already know about. This mission can actually be slightly tricky if you don't know what you're doing like I did originally.

Head to the wolf icon on your map to go talk to Edward, who once again sends you out to look for the wolf. Follow the wolf icon all the way up to a path around the lake, and the first set of wolf tracks you see that you can interact with, do so. If you don't you'll wander forever. Once you interact with the tracks, you'll be able to interact with a tuft of fur ahead up the path.

Interact with the tuft to continue, now you have to find some wolf droppings to interact with. They're right up ahead and pretty easy to see. Once you do this, you'll see a wolf up ahead and go into auto sneak mode. Do not try to stand up or run or the game will kick you back to when you first saw the wolf.

Simply keep following the wolf until your character speaks to complete the mission and unlock the achievement.