So I was Just wondering how these two cards interact with each other?

Spiritual Center states: R Commit: When an attack is gretting a speed or damage bonus, if that bonus is equal to or greater than your opponent's momentum, reduce that bonus to 0.

Hilde states: your attack gets plus X Damage and Speed. X equals double the amount your attack was reduce by during the enhance phase.

If I respond to Hilde's E with Spiritual Center do I reduce the bonus of just the damage OR the Speed or do I reduce both.

My assumption is that I reduce only one of the two bonuses, and if so am I able to respond with a second one to reduce the other?

Pretty much. Spiritual Center will stop only one of the boosts, not both.

If you use it to reduce the dmg... then who cares about the speeD?

Lord Aries said:

Cobra Blow cares. Wether they Spiritual Center or Rejection, Cobra blow can bring it right back to lethal.

Moral of the story, reduce the speed, and be sure you have the correct zone block, lol.

Cobra Blow laughs at Rejection!

Just Doin' Work said:

better hope you have the same number of cobra blows as they have rejections