are train reservations required on railjet trains btw budapest and vienna if you have a eurail global pass?
The German Rail website allows you to purchase a ticket online for the Railjet from Budapest to Munich (although it's not currently running from Salzburg to Munich, without a reservation, so I am guessing that it is also possible to go from Budapest to Vienna without one.
However, ask at the Budapest rail station before you get on. If it is required, it should be for a nominal fee.
If you're taking the RJ from Vienna to BP, reservations are not mandatory if that's what your asking. You hop on with your Pass or ticket and try to find a seat. Of course, you could get a reservation, which may be a wise decision since it could be very crowded. I've experienced that going from Vienna on the RJ to Budapest.
"btw Budapest and Vienna"? Which way are you going?
Eurail has this to say about RailJet reservations, "when traveling in or to Hungary, a reservation is mandatory."