How can I rejoin this server later in 7 Days to Die?

I don't think there is anyway at this time to achieve what you want. I have the game on the same system, and cannot find a way to do this. Since there is no defined server list to choose from, and the "servers" are really just other players hosting, its random every time from what I can tell.

Private games offer a solution to this, or hosting your own public game as well, though I have run into many issues trying to play this game online with friends due to connectivity issues. Most of the time, when I am hosting my public game, it is rare for someone to join (not sure if its because of all the problems, or because not many play the game).

I suppose the one other work around is finding out who the host is of the game, and having them invite you back. This is for obvious reasons, a nuisance though, since you're bound to another person being on at the same time.

The only way to keep rejoining a server right now is figure out who is running it and send them a friends request. That way you can keep joining.