Honestly, if I wanted to stab a character and not incapacitate them? My first thought would actually be the hand. It would restrict their use of it for a while, but it could be quickly bandaged, and it’s probably the “best" place to get stabbed.
Thing is, most places, stab wounds are non-trivial. There’s some places you can get stabbed, like the shoulder blade, where the blade will hit bone before it does anything really nasty.
But, as a guideline; three inches of penetration, nearly anywhere on the body, is a life threatening wound. That deep and the odds are unpleasantly good that you’ll hit an internal organ or an artery.
Depending on the size of the knife that’s either possible or not. But, yeah, I’d say go with the hand. It’s a nice visual injury, and if you want, it can easily become a permanent wound for your character to carry with them. It’s easy to get the hand in the path of the knife without much work. And, it’s one of the few stab wounds you can really walk away from.