Hello. Wher do you live? And where in Norway you will go. If you look up the Norwegian sides of Vy,,then you finding everything about train station in Norway. Don't forget pulpit rock ( Prekestolen) outside of my hometown Stavanger. Have a great time .

Several Routes are possible 

I use often Bahn.de and the local railplanner Websites :) 

All train Routes  can be via Stockholm to Narvik (North Norway) or via Östersund to Trondheim or Stockholm- Oslo directly (actual not in Operation) or the last option via Gothemburg to Oslo. 

Another way could be by ferry to example Bergen from Hirtshals Denmark some of them offer special discounts for Railpass User 

I live in the Netherlands and I was mainly wondering how you can cross the sea

There are ferries from several Danish ports or you use the Öresundbridge in Transit via Sweden Göteborg to Norway 

I haven't checked for your specific requirements but the Man in Seat 61 at https://www.seat61.com/ has lots of helpful information, including ferry connections, on train travel anywhere, .

Happy travelling :)

Travel from Denmark (via Sweden) to Norway is possible by train throughout. Swedish Railways (SJ) run direct trains at least every 1-2 hours across the sea bridge, most of these stop at Malmo, where you can change trains and travel via Gothenberg to Norway. The international trains are classified as Snabbtag (Sn) and attract a supplement. 

There are local trains too, that run direct to Gothenberg (Góteborg) ran by Otag, these slower trains run every hour.  

There are multiple options where you can cross the sea, depending on where and if you want to stay overnight along the way:

• NL - Kiel | overnight ferry to Göteborg (Stena Line) | Göteborg - Oslo 
• NL - Aarhus | stay overnight in Aarhus | Aarhus - Hirtshals, then ferry to Kristiansand (Fjord Line) | stay overnight in Kristiansand, continue next to for example Stavanger on the scenic Sørlandsbanen
• NL - Aarhus | stay overnight in Aarhus | Aarhus - Hirtshals, then ferry to Stavanger or Bergen (Fjord Line)
• NL - Aarhus | stay overnight in Aarhus | Aarhus - Frederikshavn, then ferry to Oslo (Fjord Line)
• NL - Copenhagen | stay overnight in Copenhagen | Copenhagen - Oslo (both long trips, Sweden section not yet available in planner due to coronavirus) Or, if you want shorter journeys, consider a stopover in Odense or Göteborg.