If I take a train from Milan to Paris using my rail pass do I have to purchase a ticket for the part of the trip that goes through Switzerland? If so, how do I do that? It is NOT a night train, which I now understand doesn't allow a rail pass anyway. Thanks.
Depends which countries are on your rail pass and which countries you are travelling through.
If you are travelling using a rail pass, it has to be valid in all countries and on all routes you intend to travel on. Otherwise you need to buy a ticket for the missing segment.
If your train is going directly from Italy to France without going via Switzerland, then you only need a pass for Italy and France. If the train is going via Switzerland, you need a pass valid for Italy, Switzerland and France, or a ticket.
You can buy tickets for Switzerland on the Swiss Federal Railways website: www.sbb.ch
Also, if you are travelling on a TGV (High Speed Train) in France and using a rail pass, you need to pay a supplement.
The direct TGV that runs twice per day from Paris to Milan does not cross Switzerland. If your pass covers France and Italy, then you just need a seat reservation, and should book that well in advance, probably 1-3 months ahead, since the number of reservations for pass holders is limited. Booking it at the same time that you buy the rail pass makes sense. The overnight Thello-brand train on this route does not accept rail passes, but offers a 20% discount; if you want the overnight train, booking ahead will give you the better price; it also does not cross Switzerland.
If you choose a train route via Switzerland, then it will include connections at a Swiss station, and you will either have to buy separate tickets for the Swiss portion of the trip or include Switzerland on your rail pass.