You can go (roughly) via France or via Germany.
It’ll take about two days, so you’ll neet to split it up somewhere in the middle. So depends if you want to visit something kinda on the way in France, Germany, Switzerland and maybe Austria.
Depends what you value, the pass gives you flexibility to make as much detours as you want.Scenic routes, places you’ve always wanted to see. All possible.
France is quicker, but more expensive when it comes to reservations and they are mandatory. Usually very comfy seats in 1st class, but not much of a service otherwise.
Germany is slightly slower, but trains are more frequent reservations are optional and cheaper. Seats in 1st class are good, and the service is also better (Usually you can order a bit of catering at your seat)