what is the jokers goal?

I’m not really into all that superhero / Batman stuff, but I think I can offer an answer all the same:

Most people are destroyers, not creators. It is much easier to criticize, tear down, dispute, invalidate, or otherwise destroy other people’s ideas, works, and systems than it is to conceive, implement, maintain, and defend your own.

It’s a miserable way to exist, and the Joker seems like exactly such a creature.