It's dependent upon what model bike, and exhaust. It's not good idea though, as they are designed for a specific amount of back pressure = power. Typically, a one inch punch and a hammer will punch through, though some new models require a hole saw. The bike won't run well afterwards though, it may also be illegal in your state.
I could tell you but it is not a good idea. If you want a louder exhaust just go and buy a aftermarket slip on. When you punch out a stock can it tends to ruin the sound of the motorcycle. You might as well just punch a hole in the side of the can.
Punching baffles involves getting a long metal pipe and for each exhaust pipe, punching through the plate end of the baffle. Some use a hole drill to do this. Either way, your pipes will sound great!!!!