There's no hard knock downs in this game, but you have ways to basically force the opponent to stay put.
For instance, certain moves will pick up rolling characters off the floor (or just hit them out of the roll) and let you combo. So, if you knock them down, and they try to roll away, you could use that move and start a whole new combo until they decide to stop giving you free hits and just tech up in place.
Basically, it's kind of a guessing game, but you want to train your opponent to tech the way you want them to.
Actually, there are SOME moves that basically do that, but they're exceptions. Tager's Gadget Finger and Ragna's 22C both immobilize the opponent and force them to have a SF style wakeup.