Please check the timetables on www.sbb.ch. Panoramic expres trains will be marked “PE”. "Belle Époque” style coaches are also mentioned when they're on the train.
If you have a pass, you're free to make whichever journeys you want. You can board and alight from these trains at any scheduled stop, multiple times if you want. Just record all trains in the app (or on the pass cover for a paper pass).
Seat reservation is not necessary as far as I know; there should always be a few coaches that can be used without reservations.
"Belle Époque” means there are coaches in the Belle Époque style:
https://journey.mob.ch/en/stories/belle-epoque
Panoramic means here will be coaches with panoramic windows:
https://mob.ch/activity/goldenpass-panoramic/?lang=en