Hit Me Again!

Question: With the knack Never Say Die, do you use pre-soak damage successes or post soak damage successes to establish the Willpower restored?

Never Say Die grants Willpower equal to the damage taken, as it says pretty clearly; that's the damage the character actually suffers, not the raw pre-soak damage that mostly won't make it through his defenses. You're impressing and uplifting others with your ability to take a licking and keep on ticking; they're only impressed by the licking you actually take.