your purpose is like passion inside you, a fire that won't be put out, the thing you imagine doing that brings you extreme joy when you think of it.
keep trying different things until until you find you purpose.
I've been asking myself that same question for a very long time... lately I'm realising that you don't... It finds you.
Find something you are moved by or passionate about, and make it a purpose to participate in and be part of it!