Well.... you meet him in a couple of places(since he's a thief that moves a lot):
first time you've seen him, he's called Alleyway Jack, in Alexandria, in the utter beginning of the game (he's the guy that explains Tetra Master)
second time he's in Treno, when you're back from Alexandria taking a break (he's in the seq. involving Eiko/Quina/Amarant)
third time you can meet him is in Daguerreo. When you speak to him, you can ask what your thief skill is, or you can play cards with him. The cardgame with him is special, 'cause he only plays with airship cards(and since i collected every card in the game, i played against him a lot; just for the invincible and others
)