Does Note8 support IP68 without S Pen?

Yes, S Pen storage area is also tightly sealed and support IP68 level without S-Pen. 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.