Clarification about Trauma please.

So i was theorycrafting a build and i wanted to know :

Boneshatter's tooltip says "2% more damage per Trauma"

And the Trauma buff state : "Some Strike skills gain bonuses for each Trauma you have"

So what exactly is the bonus? does the Trauma bonus give a flat "more damage" or does it only gives the bonus to boneshatter and strikes with trauma support?

Does the "2% more damage" apply to all global damage i do? would spells gain a bonus too?