Best way is to get the underground to centraal station it’s only three stops and cost £5 and change. Then from centraal station it’s a free ferry ride to the hotel. It’s the platform furthest left says NDSM wherf
From the airport it's quite a distance, but taking the train to Central Station is indeed the easiest option like Paul already told.
Very easy to get from Schiphol airport to the hotel. Take the train from the airport station to Centraal Station. Then just walk out of the station on the river side to the ferry (no more than fifty meters). There are three ferries, the one to NDSM Wharf is clearly marked and leaves at 30 minute intervals (15min and 45min past each hour).
Just add to my comments that when you get to Centraal Station, follow the little boat signs that are clearly displayed overhead to get to the ferry. The ferry is free so you don't need to worry about getting a ticket. The boat ride to NDSM Wharf takes ten minutes. When you arrive, the hotel is clearly visible about 150meters away on the other side of a car park. The is probably one of the most hassle free airport to hotel trips that exist.
Get an answer from DoubleTree by Hilton Hotel Amsterdam - NDSM Wharf staff and past guests.