How early to get to train station?

It depends on who you're traveling with. My wife shoots for at least a half hour before I'd want to get there, which for a reserved seat is just as the train is pulling away.

If you're asking about security checkpoint delays, a quick use of the search engine above will point you to some recent threads on the subject.

Train stations in Europe are not like airports. If you have a ticket with seat reservations, you can show up and board just before it leaves. There's no security to go through. Usually, 15-20 minutes prior to departure or whatever cushion gives you peace of mind is just fine.

For trains without seat reservations, which are the regional locals, you might want to get there a bit earlier as it's first come first served on picking seats.

Also, the arrival/departure track is not posted until 30 minutes prior to departure and I have seen it posted as late as 5 to 10 minutes. There are big schedule sheets posted under glass that indicates the normal track number but it is subject to change and to change at the last minute. Therefore, little value in being at the station much before 30 minutes.

Altho there is no security check on most lines, Spain puts you thru a security check for various trains heading to Madrid. We are not aware of any checks in Italy, as we have never been subjected to such things in scores of train journeys

Keep in mind that for most trains the quai wont be posted until 20-30 minutes before you leave. The only reason to get there with plenty of time is if you have luggage. Often if there are many people travelling there can be a rush for luggage space. (People are given reservations based on their destination so if the train stops at little stops but most people are travelling to the terminus most luggage will be there).

Keep in mind just because you travel with one bag doesn't mean the Europeans/other travellers do.