It's not Knock Knock, BUT:
I use the Gravity Screen app. On stock settings, it will turn off your display when you cover the proximity sensor and you tilt the device a certain angle, like when you're putting it in your pocket.
It will wake it up again once the prox sensor detects that nothing's covering it, like when you take it out of a pocket, or flip open a wallet case. You can play with the different settings to make it work however you want.
In my case, I've set it up so that if my phone is lying on the table, I can just tap/hover a finger (or palm/entire hand) over the proximity sensor and the screen will activate. Just like Samsung's implementation, or indeed Knock Knock. In my case though, it just takes one...knock.
No more wear on the power button. For turning the screen off, I use the Screen Off app (double tap with Nova's gestures). Or if I'm putting the phone in my pocket, the screen turns off automatically once the top part goes down a certain angle.
Hope this helps.