This creature gets +2/+2 for each Aura attached to it.
Whenever you cast an Aura spell, you may draw a card.
If you cast an Aura spell, Kor Spiritdancer's second ability triggers and goes on the stack on top of it. The ability will resolve before the spell does.
The second ability triggers when you cast any Aura spell, not just one that targets Kor Spiritdancer.