In retrospect I should probably have mentioned GainedJP Up (old name once again). IMO you should always have this equipped on all characters. It doubles the Jp you earn. And in this games I find the abilities you learn to be way more helpful than your levels.

Whenever you perform an action successfully you gain Exp and Jp.

The amount of exp is determined by the level of the target you performed it to. If the target is the same level it is 10exp, and add or subtract one exp for every level the target is above or bellow the characters level. (ex: Ramza lv12 attacks a lv10 enemy. Ramza gets 8 exp. Ramza lv12 heals a lv14 part memeber, Ramza gets 12 exp) You also get a 10exp bonus if your attack kills an enemy.

You also get Jp for performing a successful action. The amount of Jp gained is proportional to your job level in that class. The higher the job level the more you gain, regardless of what action you performed or who you performed it on. Also there is a small amount of spill over to other party members. So every time you Knight acts your Chemist will get a small amount of Jp towards their knight class. This accumulates even if you haven't unlocked the class for that character yet.

EDIT: Oh yeah, find treasure is kind of worthless. At the end game you use it to find the best gear in the game, but prior to that I don't really think you can get any good use out of it.