I have a question about the class weapon Skinning Knife etc, if I roll and get no surges do i get automatic gain the surge because of what the card says?

"If the target has any
number of damage
tokens, this attack
gains:

Surge: +3 Damage"

The card doesn't say you gain a surge, it says that you can use a surge to gain +3 damage. So if you get no surge on the dice roll then you cannot use this ability.

This means that you can only use the surge ability if the target has damage. Like a condition modifier.

So if attacking a target with zero damage with this knife and you roll a surge you could not spend it.

You not spend it on this ability ... you could always use it for other abilities/powers if available like recovering one [fatigue]