It's supposed to be hard-wired to its own 20 Amp circuit breaker. Whether it is or not depends on who installed it.

If you are handy with a meter, you can spot the right breaker by opening the electrical box under the dishwasher. You don't necessarily have to disconnect anything (I don't recommend it anyway!). Just insert a probe of the meter (Make sure it's set to the 200VAC range) into the wire-nut (cap) with the black wire; and the other into the white connector.

If you get a reading (I usually get someone to help by flipping breakers off until the right one is found), turn off the appropriate breaker, and mark its number with a permanent marker, on the cover plate.

If you don't get a reading for voltage, go to the breaker box and look for a tripped breaker. It won't be flipped all the way to the off position, but its position will be easy to spot, compared with the others.