Galaxy Note9: Does S Pen support the resistance of IP68 level?

Yes, the S Pen has an IP68 rating, which means it's water-resistant. But sometimes, if it gets wet, there might be a little bit of water left near the tip. When this happens, pressing the S Pen can feel hard. To fix this, gently clean the S Pen with a soft cloth after getting it wet, then let it dry completely before you use it again. 

For quicker drying, try holding the S Pen with its tip pointing down and give it a gentle shake a few times. This helps remove extra water inside.

Alternatively, you can blow cool air on it until it's totally dry. If you're still having issues, visit a Samsung contact center. They'll know what to do!