Does Note8 S Pen support IP68?

Yes, Supporting IP68 both in Note8 Device and S-Pen. As S Pen is sealed by Rubber & Silicon, it also support the water-resistance of IP68 level. If you get splashed or caught in the rain, you can carry on using your Galaxy Note8 because it's water and dust resistant. 

NOTE: Galaxy Note8 and S Pen are rated IP68, meaning they are both protected against dust ingress and are water resistant. Water resistance rating is based on test conditions of submersion in up to 1.5 m of fresh water for up to 30 mins.