Train to Trier

Do you mean like a boat or a bus? You can drive yourself of course, but the train is going to be the easiest way.

Some of the DB suggestions do involve a bus and a train, other routes have one or 2 changes. Best route looks like the train that goes to Koblenz and then switch to the train that goes to Trier. That way you get to see the Rhine as this VIA train runs right along the river. Whatever way you choose, it is going to be about 3 hours or more. Just enjoy the ride. Per person, costs are around 40 €, so a car service is pretty over-priced.

I'd consider a scenic train ride one of the easier things you could do on that jet-lagged flight arrival day. Train connections are not particularly difficult (pack light) and don't need reservations. How to Look Up Train Schedules Online gives you the DB train schedule link and tips for using it.

German Rail now runs an express IC bus from Frankfurt Hbf to Luxembourg via Frankfurt Flughafen, Hahn Flughafen (RyanAir), and Trier. The trip from Frankfurt Hbf to Trier costs 14€ and takes about 3 hours. Here's the schedule. Not quite as often as the train but faster and less expensive. One change at Hahn.