"Ruin Your Plans, Vile One (Damage) Drax can use Probability Control, but only when the character chosen for his trait makes an attack roll."

Maybe a dumb question, does this mean I can only re-roll MY attacks or an opponents attack? Or either one?

You can only use his Probability Control on the attack roll made by the character chosen with his Trait.

Your opponent's attack.

It's pretty clear that you can only use the PC "only when the character chosen for his trait makes an attack roll."

The "character chosen" is the opposing figure.

Very nice. Thank you, guys!