You can take any train between Italy and Lugano that stops in Chiasso. No need to get off. I'd recommend using SBB website/app for the Swiss leg = a ticket between Chiasso and Lugano.

3. Basically all routes operated by Trenitalia (at least) but don't quote me on that.

4. Yes you will need a seat reservation for high speed trains, it's 10€ per seat (should be bought at ÖBB, the Austrian Railways). But there are often reservation-free alternatives, usually requiring more changes and a longer travel time.

Here's the list of all rail companies participating in Eurail:

https://www.eurail.com/en/get-inspired/trains-europe/useful-train-information/participating-railway-companies

Thank you so much for the info.

@thibcabe Just wanted to confirm again regarding your comment on train from Como to Lugano;

1. You mentioned that I don`t need to get off the train when I arrive in Chiasso..? Having said that, I would assume the train I board from Lake Como continues to Lugano…? Does it mean I need to buy a separate ticket online in advance for my trip from Chiasso to Lugano..? Do I need to validate the ticket at the train or there will be an officer on the train validating the ticket..? Just try to understand how the ticketing system works. From my experience overseas, I need to tap on/off (validate) my ticket at the station gate before getting on every train. Can you please explain, I am a little confused.
2. Is there any apps I can use to check train timetable in Italy that is covered by Eurail Italy Pass...?
3. I assume inner city trains do not require reservation as they are regular trains (not high speed trains)..am I right ..?

@rvdborgt not sure if my message here goes to private message..? I thought posted it via forum tab. I am not sure how this website work. Apologise if it did go through private message. Please advise.

My experience is different than yours... For me it's unusual to tap in/validate your ticket somewhere !

In Switzerland there are no gates or anything. You can stay on the train no problem. A ticket inspector might or might not come and you simply show him your ticket.

Yes I recommend buying a ticket in advance on SBB website/app for travelling between Chiasso and Lugano. The fare is 9.40 CHF one-way, the ticket is valid 2 hours on all trains, buses + the funicular down to the lake and the city center in Lugano.

For 18.80 CHF (the same price as a return ticket) the ticket is valid all day on all trains, buses, etc. of the selected zones (if necessary). 

Switzerland is divided into "fare networks" so for all travels within the Italian-speaking part you'll get Arcobaleno tickets valid on all trains and buses.

2. I don't know a timetable that would tell you if the Italy Eurail Pass is valid or not but the vast majority of the railway lines are included, no need to worry. If someone could help if there are exceptions though.

3. Regional trains are reservation-free yes but I don't know what you mean by inner-city trains. The subways are not included if that's what you meant. 

Let me know if you have any other question.

@thibcabe Thank you.

What about buses and trams, are they covered by Eurail Italy Pass..?

Cheers.

No, since they are not operated by the participating companies.