Okay so you have enough pass days I believe.
Look at https://www.seat61.com/interrail-and-eurail-reservations.htm
Fast and high-speed trains require reservations in Italy.
To get to Rome or Venice you'll have to go through Milan anyway so the cities' order depends on your wishes, where you can get accommodation, etc.
Use planners. You can take reservation-free regional trains between Domodossola and Milan (infrequent) or between Lugano and Milan (hourly). Afterwards you'll require reservations anyway.
Italy - Paris is a very long travel day. I'd start the day in Milan to make it manageable. For example :
- EC Milano Centrale - Geneva 08:20 - 12:21 (+ frequent 20 min delay) 13€ reservation
- TER Geneva - Bellegarde 13:14 - 13:46*
- TGV Bellegarde - Paris Gare de Lyon 15:02 - 17:42 10-20€
Also possible to board the TGV in Geneva right away (14:29) but it costs 29€ per person.
*times might be different due to works.
Definitely more routes possible but they'll take longer. Look at planners. Only one example via Basel/Strasbourg :
- RE Milano Centrale - Lugano 09:43 - 10:58
- straightforward connection and the EC will wait a few minutes if needed
- EC Lugano - Basel SBB 11:02 - 14:56
- TER Basel SBB - Strasbourg 15:21 - 16:39 or 15:51 - 17:09
- TGV Strasbourg - Paris-Est 17:19 - 19:06 10-20€
Btw are you going straight to CDG Airport ? It will be better to take a TGV from Strasbourg directly to the airport, direct and avoid the annoying time lost in Paris city center.
@thibcabe esse é o grande lema. Tenho 5 dias apenas.
Amanhã utilizarei de berna para italia (1 passe)
Daí vou ter que me virar para usar os transportes internos da Itália como de Roma para Veneza.
Outro trajeto: Roma ou Veneza - Paris (de onde conseguir melhor rota)
Enfim
Sabe me dizer qual melhor percurso e se tem gratuito de Berna para alguns ponto lá na Itália? Pode ser MIlao, Veneza, Roma...
It is not possible to extend a pass to more travel days.
The pass is only valid in trains, not in metro, tram or bus (except a few exceptions and rail replacement buses). So when you're in Rome, you can't use it to go to te Vatican.
You can use your pass on the other routes you mentioned.
Transportation within cities is not included in Eurail : subway, buses, trams,...
Going to Vatican should be quite cheap anyway. I'm not familiar with Rome public transport so I can't help.
How many pass days have you left ? It is not possible to add more days to an activated pass but you can get regular tickets separately if needed. :)
Venice <-> Rome will be the cheapest journey on your list. Check advance fares on trenitalia.com and italotreno.it.
Btw where are you heading in France ? Paris ? It will be a very long journey so you should leave early and book mandatory reservations in advance.