If I have a second class Eurail pass, am I able to select the train and time most convenient? I am taking a trip in October to Amsterdam, Hamburg and Copenhagen. I'll be traveling by train between cities.
Check with the Man in Seat 61
The whole point of the Eurail Pass is that you can indeed just select what train you want to take at the last moment. So in the app just look up the schedule, add it to your trip and the app will activate a day. That will produce a QR code, and that you show to the train conductors on board.
Note however that if you are able to fix your plans you probably can save a lot of money just buying tickets. Do this on www.bahn.de in this case.
My personal experience is that a second class pass seldom makes economic sense, but a first class pass often does. Also, an unlimited pass is more likely to save money than one providing a set number of trips, assuming one has a large number of trips planned. But everyone should run the numbers for their specific desired itinerary.