It's doable, but only staying one night in Florence and Venice? It seems like a lot of travel! I would maybe skip Milan. I guess in all that time in Geneva, you're going to explore Switzerland? Geneva itself is not worth a stop on such a busy itinerary.

you'll need reservations on most of these trains.

The Eurostar and the TGV are both quite expensive - around the €30-40 mark, and they have a limited quota for passholders. So check availability for these first.

The Italian domestic trains are easier. Still €13 for the high speed trains, but easy to get.

You can get reservations for the Eurostar here

https://www.b-europe.com/EN/Booking/Pass#TravelWish

Paris-Geneva via the Eurail reservations service. But see my next reply for a different option.

Switzerland - Italy, and Italy domestic trains here. Add your pass where it says 1x adult, and then search for 'one way tickets and day tickets'

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

Rome to Prague, it depends which route you take, but you'll need reservations within Italy, and crossing from Italy to Switzerland or Austria, as above on ÖBB. No reservations needed within Switzerland or Austria.

No reservations needed Prague-Berlin (but highly recommended). Same with domestic trains within Germany, and Germany-Brussels. You can get these on the ÖBB website (search for seat reservations), or the DB website.

From Berlin, youcan also take the sleeper to Brussels, to connect with the Eurostar. You buy the reservation from 

https://www.europeansleeper.eu/en

As I said in my first reply, I wouldn't necessarily recommend Geneva unless you have a specific reason to be there. There are better options in Switzerland.

I would probably base myself in Bern for a few days instead. You can take a direct TGV from Paris to Basel for €29, then a Swiss train (no reservation needed) to Bern. Or you can take a TGV to Strasbourg or Mulhouse (€10 or 20), then a TER to Basel (no reservation needed).

If you do decide to go to Geneva, then there's a similar approach. The direct TGV from Paris costs €29 reservation fee, but if you take the same train and only reserve as far as Bellegarde in France, it will cost €10 or 20. You can take a TER from there to Geneva.

The TGV straight to Switzerland has to be reserved through the Eurail reservations service, I think. But the French domestic TGV are better reserved here:

https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish

Very complete answer above ! In addition :

I'd go to Amsterdam at the end of the trip unless there's a specific reason to go there in December. It make more sense when you look at a map : there are direct Berlin - Amsterdam trains and a few direct Amsterdam - London Eurostar (more with a change in Rotterdam or Brussels).

Geneva is also not a good base for Switzerland : it's expensive and well out of the way of the rest of the country. I'd consider Bern too.

I'd skip Milan and have more time in Florence.

Rome - Prague is a very long journey, probably not doable in a day. I'd consider either the Rome - Vienna or Zurich - Prague night train. With a Eurail Pass you only pay accommodation price (seat, couchette, sleeper).