Hey, you need reservations for high speed trains in Italy (Frecciarossa, -argento and -bianca - 10€) and for IC 3€. RV/RE and R do not need reservations (also not possible). EC Italy-Switzerland costs 11€ in 2nd class), 10€ within Italy. 

You can’t book your reservation online via Trenitalia.com but only via Austrian Railways ÖBB (oebb.at - one way ticket option, add discount Interrail/Eurail Globalpass, you can book all reservations but not for Nighttrains ICN) or Interrail.eu (+2€ fee)

You can also book at ticket offices of Trenitalia in Italy, SBB CFF FFS in Switzerland or also at DB, ÖBB and SNCB/NMBS. 

Is it possible the OP is asking about the Trenitalia Pass? https://www.trenitalia.com/en/offers/trenitalia-pass.html

Reservations for that are free and can be made at the Trenitalia website (funny how they can make it easy and straightforward when they want to) unlike Interrail passes.

Think money-as is nearly always the explanation of what outsiders think of as being funny;

what tr_It sells itself gets in their pockets.

What others sell in the end they get a portion of-as there are also other operators who share in the takings.

Same applies to ESpana-there the difference is even bigger (and also there is no competitor)-RENFE also has a same kind of online-only pass.

Tr-It ALSO has a very cheap 3 or 5 day pass for ONLY its local treni.

Yeah the strange thing is that this pass came on the market when the Interrail Italy OneCountryPremiumPasses (that where exactly like the Trenitliapass) disappeard.

From Friday i will test the Trenitliapass (the good thing is here you can buy it for all comfort levels and even the Nighttrain reservations are covered )