This one can take a while, as it's highly dependant on RNG, but there are a couple of tools we can use to make it easier.
Basically you need to be on one of the four Woods spaces, draw a Wolf enemy from the deck, and win in a Battle against it. There are three Woods spaces in the Outer Region(north, south, and west), and one in the Middle Region(east).
As the Woodsman you get the option to draw one extra card from the deck when on a Woods space, so make sure you always do this to maximize the chance of encountering a Wolf.
Try to avoid Woods spaces that have cards on them already, especially cards that don't go away. If you have the means to do so(f.ex. through the Destruction spell), remove such cards from the Woods spaces.
Getting the Poltergeist follower will make life a lot easier for you, as it allows you to move back and forth between two spaces. So make sure you don't cross the river while having the Poltergeist(teleporting is fine). If one of the spaces next to the Woods space you're using in this manner has cards on it, that will lessen the chance of encountering a Wolf while not on the correct space.
The Orb of Knowledge is a very handy item to have, as you can discard one of the cards you draw when on a Woods space, giving you another shot at drawing a Wolf if you didn't.
When you finally encounter a Wolf on a Woods space and slay it, the achievement unlocks. That's the easy part.