Are two Nintendo Switch consoles needed to play locally Ultra Street Fighter 2 with a friend? Or is it possible to play on the same screen? In that case can each player use a single Joy-Con, or does each player need a separate set of Left+Right Joy-Cons?
Yes, you can play Ultra Street Fighter 2 on the same Nintendo Switch console. For this, you'll have to connect your Nintendo Switch console to a TV. Playing in TV mode will allow you to connect USB controllers to play the game. You can also use left and right JoyCons for this. For Local Mode multiplayer, your friend should have his own Nintendo Switch console. You can get some more info on IGN's website or you can watch a video here on YouTube about how you can do it.