Hitch Mate, Hitch
Depends on the individual policy / operating laws of registry for each cargo airline. Some do take "cargo attendants" but increased security means you have to have a good reason to be on the flight, especially into the USA.
"Cargo Attendant" is the general term.
You WILL find that a jumpseat ride not possible, e.g. operating crew or inspector only. Some no UK airlines do allow this provided you work for the airline in question and are on duty.