can jannas q disrupt leonas e?

Any properly timed Knockups, Taunt effects and Charm will cancel Leona's E.

Yes, as can Nami bubble, Thresh Flay, etc.

Leonas E is a dash, so it will get interrupted by well timed(or random) displace(knockup,knockback, hook...), just like every other dash/jump/charge in this game.

Yeah but timing is tricky. Draven E can do it as well.