We will be using our pass from Trier, Germany to Bruges, Belgium and then on a later day from Bruges to Bremen, Germany. I have not done so yet and the trip starts next week. If it is needed then possibly I could make seat reservations in Franfurt on our arrival. Suggestions appreciated.
On Trier to Brugge, you will ride on a regional Deutsche Bahn train, then two separate Belgian rail trains. Most Regiobahn trains do not offer reservations, and there are no reservations on any Belgian Rail trains. You have several options from Brugge to Bremen. Some involve Thalys and all involve a Deutsche Bahn ICE (intercity express) at some point. You must have reservations for Thalys, and they limit the number of seats they offer to pass holders. I'm not certain of the rules for ICE trains and pass holder, but when I ride on an ICE, I always purchase reservations. It's not strictly necessary, but I find it much easier. I know where my seat is located, and I can walk straight to it without fumbling around looking for an opening. If you haven't yet purchased the pass... do you research first. Passes rarely save travelers any money these days.