You can make reservations at larger train stations in Europe, including ones with a Eurail aid office. Just show your Eurail pass at the ticket office and explain which train(s) you want to reserve.
In Italy, you can also make reservations at the ‘Self-service’ machines to avoid queues, including stations in Bari, Bologna, Florence, Genova, Milano, Naples, Pisa, Rome, Turin and Venice. On these machines, select the train you want to use and then click on the 'Global Pass' button (see example screenshot). You can pay the reservation fee by cash or credit card.
Being as anal as I am, I wanted to make the reservations ahead and spotted the tab on the Eurail site for on-line reservations. From there, the following was noted:
How to make online reservations
Reservations can be made on the Trenitalia website. If you want to receive an invoice of your order you'll have to register before making your reservations. If receiving an invoice isn't necessary, you can start right away.
Follow these steps to make your reservations:
1 Enter your departure city and city of arrival.
2 Choose your preferred train connection and click Select
I challenge you to find the word "reservations" on this website. I did figure out what to do, but I could never recreate it for you, and since it didn't work for me anyway, I will tell you what I did do, and what I would suggest doing. I went to a US-based company, Rail Europe, which has a slick easy-to-use website. But this process was far from clean. The problem I first incurred when trying to order reservations for the train I wanted to use was that it wasn't there. It was there for earlier dates but not for the date 3 months hence that I wanted. Why? Because the "schedule" wasn't ready yet. After emailing Rail Europe they agreed to notify me when the reservations could be ordered. But even after they were available, I still got a message from their website after making a payment that the order was in progress, and I would be contacted when reservations were available. After many emails and a phone call or two I learned that the schedules were being loaded, but for the trains I wanted to schedule they hadn't been as yet.
The above problem ultimately was resolved and I received the reservations suddenly in the mail. Hallelujah! Then as I finalized plans for the trip, there was learning about the validation process for the Eurorail pass before getting on the train. Prior to using your pass, you must have it validated at the train station. The problem is that if your train is an early one that means you have to arrive very early to have the pass validated before finding your train and getting on. According to Rick Steves you can do it a day before, but that could be problematic too -- allowing time in your itinerary for this as well as the confusion of validating before the day of your trip.
Bottom line. If you plan to travel by train, and plan to use a Eurorail pass, make sure to get your reservations, and then make sure you allow time to have your pass validated. Also I realize as I laughed over the extraordinary process involved with just getting on a train that I needed to lighten up and just accept the bureaucracy of it all and work with it. It will all fall in place -- at least I hope. Next chapter on this topic will be using the trains in Italy. I will let you know how the whole process works out.