• There is one QR code per travel day. It is generated when you add the first train of the day to your pass.
• You can add trains to your pass as you go along. You're flexible.
• Any train you use must be added to your pass. If you change plans, just remove the train(s) you won't take anymore and add your new train(s).
• In Italy, the ticket machines don't seem to sell reservations anymore. Ticket offices do; how much time you need depends on the queue… other than that, it takes a few minutes. You can also book Italian reservations online via tickets.oebb.at: do NOT use "Seat reservation only” but add the Interrail/Eurail discount and then look for normal tickets. It works similar in the OBB app.
• In France, you can also buy domestic TGV Interrail reservations from SNCF ticket machines, from the white, Grandes Lignes ones. Here you also need to select Interrail as a discount. Shortly before departure, the €10 reservations are usually nor available anymore and it will be €20, except when the train is fully booked of course, but that normally only happens around start/end of a holiday and long weekends.
• International TGV reservations are very expensive. Italy-France is not available from a ticket machine and has a limited quota for pass holders so is best booked in advance.

You'll find that some community members have been building an extensive reservations guide, which you can find here: https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

Please read it attentively, you'll find a lot of reservation information there. 

For TGV trips in France I would really recommend reserving in advance, some connections are not that frequent (they have a weird, non-cadanced train scvedule in France) and you wouldn't want to risk not being able to board. 

Any idea what you want to visit already on your route? 

Auf DE: drehscheibe-online.de - mit noch sehr viel mehr Sachwissen.

It is often fairly easy to avoid the direct TGV trains from FR to CH/IT-and also DE-by using them only as inland till last stop in FR and hop over border with local trains-this will lengthen triptime and lower cost-not possible on all routes.

Note that I found that the SNCF machines: purple/white now do NOT spit out printed tickets anymore, but want to give in tel.nr=@mail and will send a confirmaton to that mail. For many Germans this can be a rather sensitive mooted point.

IN DE=your homeland can only use on 2 days-to go out and come back in, and these  are NOT exyra days/trip, but most be done on normal traveldays.

In FR-due to protest against the rise of pension age-except again long and fierce strikes the upcoming monthes. (Im moment gehen Eisenbahner dort schon mit 54/55 im Rente……….

You get a QR code for the day after activating just one journey. You can then add other journeys on the go (add them first to your trip and then to your pass with the slider button) and can even deactivate the first journey you activated if you decide to do a different journey instead (but once the travel day has been activated for that same day the travel day cannot be cancelled).

It really depends on the situation: some stations might have a queue for ticket offices, some trains might be sold out so short before departure, ...

Reservations for Italian trains can be made online through oebb.at (see the reservations guide for a detailed guide), so if you see you're going to reach your connection you could book it through them.

I believe if Trenitalia is to blame for the delay of the previous train, they should also offer you a reservation on the next train. No experience with this, so can’t say for sure how that works out in practice.

Reservations in France increase in price depending on demand: some seats are sold at €10, but once those are sold out remaining seats are sold at €20. Since trains can sell out as well and since all these reservations can be cancelled free of charge up to the departure time (though note the booking fees charged by Interrail/b-europe are not refundable), I think it generally is a good idea to book them ahead, and cancel them if unneeded.

Domestic French reservations can be booked through the Interrail reservations portal (€2 additional fee per person), a dedicated site of the Belgian railways (€4 additional fee per booking), through SNCF telephone ticket sales and at SNCF ticket machines (no extra fee) in French stations (& in Luxembourg) and at some ticket offices (but I believe not at DB ticket offices). The Interrail reservations portal is my last choice, generally, as it is not able to sell connecting tickets.

French domestic trains do not have quotas limiting the number of passholder tickets sold for them, but the France-Germany TGV/ICE do. Book those early if you intend to take them (those can be booked through DB ticket offices).

Not as experienced travelling in Italy, so can’t say much about that. It did work pretty fine with me to book the reservations online through ÖBB.

Thank you, this is very helpful.  So I will just activate the first trip and add others as I go along on this same day.

You can also book Italian reservations online via tickets.oebb.at: do NOT use "Seat reservation only” but add the Interrail/Eurail discount and then look for normal tickets. It works similar in the OBB app.

So, there’s no problem if I use the mobile reservation, rather than anything in printed form?

No, usually not. If you plan a night train it's recommended to print the reservations, cause the attendant usually keeps it.

This only happens if they have run out of paper - I got one printed a few weeks ago. If it happens and you don't have a Smartphone, just write down the shown booking number and either walk to another machine to print them or go to the train manager - they should be able to find your booking with it.

I had no problem with that. I think I showed them the PDF on my phone, though you can possibly also get them in the ÖBB app.

As more and more operators are accepting pdf copies the problem of not having a printed reservation are disappearing. However where possible I always print out a copy or try to get one at the point of purchase. Firstly it saves changing pages on my smartphone at inspection and secondly it is much easier to show any squatters than trying to show on your phone. 

Thank You, I’ve have checked out this guide now.I should be able to get along. I decided now not to use a TGV, mostly trains without reservation except one IC from Narbonne to Marseille. But I got enough time in Narbonne the day before to check out the options and get a reservation in the station.