The damage of an attack is compared to the victim's Toughness just like a Trait roll (though it isn't one so you can't spend a Benny on it). With a success, the victim is Shaken. For each raise over his Toughness he suffers a wound as well, as shown below:

Success: The character is Shaken. If he was already Shaken, he suffers a wound and remains Shaken. To cause a wound, the latter Shaken result must come from a physical attack of some kind–not a Test of Wills or other maneuver.

Raise: The character suffers a wound for every raise on the damage roll, and is Shaken. (When wounds are caused, it doesn't matter if the victim was already Shaken beforehand.)

Damage Table

Example: A barbarian hits an ogre with a Toughness of 11. The barbarian's friend, a rogue, has already taunted the beast (a Test of Wills, see page 86) and Shaken it.

If the barbarian's damage is 11-14, that's a success and would normally Shake the ogre. Since it's already Shaken, he suffers a wound and remains Shaken. If the barbarian's damage is 15+–a raise or more–he'd simply cause wounds. The ogre is already Shaken, and since a wound was caused, there's no further effect.

Savage Worlds Deluxe Edition p. 76