Surprise Attack is a skill located in the Shadow (which can be found in the Nightblade skill tree). Surprise Attack is a morph of Veiled Strike.
Surprise Attack deals the following types of damage: Physical Damage. Which means that it gets buffed by the following blue champion point trees: Master at Arms, Mighty, Piercing, Precise Strikes. Also the following red champion point trees protect against this skill: Hardy, Iron Clad.