I don’t know of any direct sleeper from Rijeka to Frankfurt. There is one to Stuttgart.

They can been booked on oebb.at. What date are you trying to travel?

June 22nd.  Do I just put in my Euraill pass number?

Search here: https://shop.oebbtickets.at/en/ticket

And where it says ‘1 Adult No Discounts’, change it to add discount > Interrail/ Eurail.

Then click one “one way tickets and day tickets’ (not seat reservation only!)

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The only availability is for a berth in a shared 3-person sleeper, at €79.90. There’s no couchettes available.

There are also seats and couchettes if you book from Ljubljana. Rijeka-Stuttgart direct is just 1 single sleeper carriage, that is first attached to a day train Rijeka-Ljubljana and then to the night train (Zagreb-)Ljubljana-Stuttgart.

Thank you!

Thank you!

If I book it to Stuttgart, can I get off in Munich?  In other words, is there enough time for me to get off?

Yes, no problem. 

Yes you can. Best is to notify the coach attendant if you're getting off at another station than what it says on your reservation, otherwise you might miss the included breakfast.