what episode does luffy use gear 2?
Luffy first uses gear 2 against one of the CP9 members- Blueno, in the Ennies Lobby Arc. This happens in episode 272 / manga chapter 387 and 388. The scene in the episode roughly goes like this: He sees Blueno atop the Courthouse (Luffy is down a hole and not visible) and tries to figure out what is happening.