While using the Shaitan Style and Elemental Fist feats to deal acid damage, you gain a bonus on acid damage rolls equal to your Wisdom bonus. Further, if your Elemental Fist melee attack misses while you are using it to deal acid damage, you still deal 1d6 points of acid damage to your target.
Creatures that take acid damage from your Elemental Fist attack must succeed at a Reflex save (DC 10 + 1/2 your character level + your Wis modifier) or be staggered for 1 round.
Does the reflex save from Shaitan Skin trigger from the acid damage of a missed Shaitan Style + Elemental Fist attack?
No, shaitan skin does not trigger as it is not the elemental fist attack that caused the damage.