trains and gondola rides covered by 2 country eurail pass

If you have a pass you can get on and off trains as many times as you like, that is the point of a pass, In Switzerland you don't have to make a reservation or get any ticket in advance, the pass is your ticket. As long as you have the ticket with you, you can just get on the train.

Now the difficult bit. A Eurail pass has slightly less coverage in Switzerland then a Swiss Pass.
A map of Swiss railways showing what a Swiss Pass covers is here (2nd page): http://www.sbb.ch/content/dam/sbb/de/pdf/freizeit-ferien/ferien-kurztrips-schweiz/internationale-gaeste/sts-geltungsbereich_en.pdf
A list of the rail companies covered by the Eurail pass is here: http://www.eurail.com/europe-by-train/switzerland/swiss-railway-companies-included
And a map is here: https://myswissalps-doc.r.worldssl.net/docs/default-source/rail-network-maps/eurail.pdf
And yes, the Glacier Express route is covered (Chur - Andermatt - Brig - Zermatt)

Note the Glacier Express is not the only train on this route. Like all train routes in Switzerland there is one train per hour. The Glacier Express is an additional limited-stop service for tourists, but you see the same mountains out the window whichever train you take.

Thank you for all that info!

The named departure of the Glacier Express does require a seat reservation, in addition to your pass, but the other regional trains running along the same route do not.

Yes, and if you want to get off and reboard a later Glacier Express, you would need to buy a new reservation. But there is no reservation required on normal trains. Normal trains run at least once per hour and generally do not have panorama cars. They do not cover the entire Zermatt-St Mortiz run as a single train. You will have to change trains along the way, but you will see the exact same mountains as the Glacier Express. Some people even prefer the normal trains as you can open the windows for better photos, something you can't do on panorama cars.