Im a new to X-Wing and have a question, are proton torpdoes a one time use or multiple times?

As the card shows, they have 2 charges (the circle with the lightning bolt), and since the attack requires you spend 1 charge, you get 2 attacks with them.

Unless your ship has the reload action , then you can fire again, although this usually is an action that cause stress .

and unless you're using chopper astromech to regain charges or munitions failsafe to cancel the attack after rolling dice.