If I purchase an RV ticket from Verona to Venice and want to stop for a couple hours in Padova along the route. Can I do that (getting back on a later RV train, same route) without buying a new ticket? Or should I just buy a ticket to Padova. And then later a ticket from Padova to Venice?
Keep it simple buy two separate tickets.
Verona to Padova
Padova to Venice
There are plenty of self service kiosks colored red at the stations to do that.
I agree - keep it simple and buy separate tickets.
You can keep it even simpler by downloading the Trenitalia App onto your smartphone and using that to research and book your tickets - saves standing in line or having to deal with the possibility of unreliable kiosks, as well as not having to worry about validation since electronic tickets are already time stamped.
Be aware that you normally must reserve your spot for the Scrovegni Chapel in advance. I would not attempt to see it on a quick stopover without buying a ticket online in advance. In addition, there are procedures that must be followed prior to your ticketed admission time, so it's not a good plan to make the Chapel your target if you have very little time in Padua. I'm just completing a visit there. I've spent 48 hours here so far and haven't made it to the Duomo or a couple small museums I wanted to see.