Well first I’m not sure what the white abilities or powers would be considered on a character.

My question is regarding Dormammu #048 from Avengers Forever.

He has Energy Explosion, Penetrating and Knockback. Is he able to use ALL of these on one attack or just only pick one?

A character can use all and any powers and keywords granted by a special power. If they can use them at the same depends on whenever you can combine the power (in the case of P/PB and EE you can, but couldn't in the past. In some cases like for example HSS and Flurry, you can't).