From San Sebastián, you need to get the Eusoktren (not included in the pass, I think) to Hendaye. I would book Hendaye-Paris via the Interrail site https://www.interrail.eu/en/book-reservations#/login It’s not the cheapest, but it’s the easiest.
Paris - Amsterdam - book at Interrail or B-Europe for the Thalys, or take regional trains (Much, much slower) if you really want to avoid the fees. https://www.b-europe.com/EN/Booking/Pass#TravelWish
The others you can book on ÖBB. https://shop.oebbtickets.at/en/ticket Reservations are optional on Munich-Salzburg.
There are other options - details below (along with instructions): But I think those are what I’d use.