Not a jumper in AQHA, but a AQHA member nonetheless.
This is where you'll find your class level: AQHA: Leveling Program
Working Hunter: AQHA Handbook
Jumping: AQHA Handbook
(I don't know much about jumping, from what I know a working hunter is almost the same thing as jumping except one is based off your position? If those two aren't what you are looking for here is the whole selection of English events from AQHA: AQHA Handbook
Those two will give you the rules on the scoring, how the course is set up, etc.
English Equipment: AQHA Handbook
Here is English Attire (note that English section is the 3rd rule down): AQHA Handbook
That's all I have, good luck! (: