I have have no momentum?

Its static ability reads: " If this attack deals damage. discard 2 of yoru momentum."

Im pretty sure if I were to have 2 momentum, I would have to discard it regardless, but I was wonder if this attack could still be played if I had no momentum before...or even after it deals damage?

yes you can

if you couldnt it would have said "as an additional cost to playing this card, discard 2 momentum" like Kogu-Koguretsusan

it's not the cost of playing the card as cards like Shadow Hunter are so it'll only come into effect if it deals damage, do note though if it deals damage you will discard any momentum you got until you either run out of satisfuy the 2 momentum.

N.J.

Stampitude. This falls under "Do as much as you can" since it isn't a cost for anything.