Aug 14, 2017 - 7:00 AM
in reply to Giselapina
No, you can buy the ticket in advance, no need to get off the train at Chiasso.
You can take a direct train from Zurich to Milan. You just need to have a ticket to cover the route after Chiasso.
IE you can take the 09:09 train from Zurich that leaves Chiasso at 11:52am. Use the rail timetable here. The ticket for the 11:52 train from Chiasso to Milan can be bought on the link in my first post.
If you are asked for a ticket you can show the Swiss Travel Pass anytime before Chiasso. If asked for a ticket after Chiasso show them the individual ticket you bought online.