How can I find the circuit breaker that my outdoor outlet is on?
The first thing to check since this is an outdoor outlet is to see if there is a GFCI device built-in ("test" and "reset" buttons on the outlet). The GFCI may have cut power to the outlet. Sometimes several outlets are connected to a single GFCI so if there isn't one at that outlet look for others nearby. All outdoor outlets are required to have GFCI protection since the 1970s, although sometimes older homes haven't been updated.

If the GFCI is fine or you can't find one, next check the breaker panel. A breaker that is tripped should is identifiable because the switch is in the middle (neither ON nor OFF). However sometimes it can be difficult to tell, especially with older breakers that have a little bit of wiggle.

The easiest thing to do is to turn them all fully OFF and then ON, one by one. Alternately, some circuit breakers have the GFCI built into them, so try the "Reset" button if you see one.

Once you have identified the breaker, update the label next to it so that you don't have to guess next time.

If you can't find a breaker that restores power, check for a sub-panel somewhere and/or double-check for a GFCI (could be somewhere unusual).

(Bonus tip: if you are trying to identify the breaker for an outlet that works, plug something loud into it: a radio or a vacuum cleaner turned on. Then when you are at the panel you can hear the sound stop when you have flipped off the correct breaker.)