Make sure you have The City DLC purchased, or it's on rotation for free trial, and activated for the game. Choose the Tinkerer as your character.
Walk around in the City space until you encounter a Clockwork type enemy, then defeat it in battle, and choose to keep the trophy. (Make sure you don't turn it into a follower at any point!) This will unlock the achievement.
PS: I've had trouble getting this to work with the Clockwork Dragon, and I'm assuming it's a bug related to how you can choose to get a Talisman from it instead(which I didn't do). Also, there aren't many Clockwork type enemies in the City deck, but if you have the Clockwork Kingdom DLC, that should make it easier to find Clockwork type enemies, and make this much quicker! (It can take quite some time with only The City, unless you get lucky with the cards and the rolls.)