Eurorail

You probably need to change trains. Please check on the website of austrian railways for the timetable.

scotty.oebb.at or ÖBB Scotty App

As already mentioned the ÖBB travel planner Scotty is the best source for your requests. It usually gives a lot of connections, so you need to filter or disregard that ones where you need to change trains twice or a bus is involved.

Between Vienna and Zell am See the Westbahn company (westbahn.at/en/) operates three times a day a direct train (final destination Saalfelden) via Salzburg. Note the departure station of Westbahn trains in Vienna is the Westbahnhof (Wien Westbahnhof in timetables).

Connections with changing trains is also not a big deal. In the morning Westbahn trains calling in Salzburg depart every 30 minutes, in the afternoon every hour. From the Vienna main station (Wien Hauptbahnhof) ÖBB railjet trains depart also about every 30 minutes to Salzburg. From Salzburg ÖBB regional trains depart every hour, ÖBB interregio trains every two hours to Zell am See (final destinations are Saalfelden and Wörgl, respectively).

To go from Zell am See to Munich I recommend to go via Wörgl and change there to a railjet or ICE to Munich. Going vie Salzburg would also be an option, but the travel time is longer and the Salzburg - Munich line might be affected by engineering works. A direct train between Zell am See and Munich runs only on some weekends and holidays.

If you use a first class eurail pass note that it will be valid only in standard class (second class) of Westbahn trains and regional trains are second class only. Seat reservation is not compulsory on any train mentioned here. Dependent of the date and time of travel seat reservations, which can be bought on the websites of the relevant railway companies might be useful. Eurail charges an additional booking fee and the rail planner is not always up to date. If you are several people travelling together I would recommend seat reservations in ÖBB railjets, ICEs, and Westbahn trains. In regional trains seat reservations are not possible and I do not know if set reservations might be useful in ÖBB interregio trains between Salzburg and Zell am See. In the dual level cars of Westbahn is very limited space for luggage in the upper deck.