The SNCF app doesn't support tickets from external partners (here Eurail or B-Europe). Just have the pdf at hand when you need to show the reservation before boarding the train.

Never tried it for Italian trains at ÖBB, but if you make reservations at ÖBB for a ÖBB train, you can choose for either a pdf or show it in the app when you make the reservations.

If you make reservations via DB, for DB trains, reservations also show in the DB Navigator app.

Thank you.
What do you mean by this?

I need to make two seat reservations: 1) from Domodosola to Milano, and 2) from Milano to Venezia.

I should never make seat reservation on OBB??
Then, do you advise me to make seat reservation on Eurail.com?
 

Via ÖBB you get PDF Tickets for Italy or you print it. Possible is also to print it IN AUSTRIA at ticket machines.

Thank you.
What do you mean by this?

 

I need to make two seat reservations: 1) from Domodosola to Milano, and 2) from Milano to Venezia.

I should never make seat reservation on OBB??
Then, do you advise me to make seat reservation on Eurail.com?
 

I said I have never reserved seats in Italy via ÖBB, so I don’t know if it shows in the app. But @Angelo now stated that it’s not possible, you only get a pdf or you can print it at Austrian ÖBB ticket machines. Nor did I advise you not to book at ÖBB.

If you want to save a bit of money, there are a lot of better options to reserve seats than Eurail.

ÖBB is the place to book :)

Don't worry, whenever asked you show both the app (ticket) and the PDF (seat reservation).