If a Pokemon has no Weakness to begin with, does Oranguru's "Now You're in My Power" attack give it a Weakness to {C}?
Yes. If a Pokemon has no Weakness printed on the card, Oranguru's attack will give that Pokemon a x2 Weakness of Colorless.
Source: Surging Sparks FAQ; TPCi Rules Team (2024-11-07)
Does Oranguru's "Now You're in My Power" attack mean the Defending Pokemon is now weak to all types?
No, not all types. It only makes it weak to Colorless Type Pokemon.
Source: Surging Sparks FAQ; TPCi Rules Team (2024-11-07)