What is JP used for in Grand Theft Auto Online?
JP are indeed job points. As of now - they are used to determine tiebreakers. They are shown in the list of players and reset to 0 after every session.
There is not much information on JP.
Some call it Job Points, others Judge Points.
The only thing I could muster was a theory.
Since you lose JP every time you die or lose a game mode, can be considered a score of consecutive victories to determine your ranking in the Playlist, and other players can judge you if you are a good choice for the amount of JP.