Hello InMind!
So if I’m correct you can’t find the controller for the knees direction. The lack of a poleVector may be confusing the first time you approach this, i know.
So, into the Animation Interface you can find a little box on the knees, changing the value inside the box modifies the bending direction of the leg:
A quick tip: You can press CTRL + Middle Mouse Button over the box (keep them pressed) and drag your mouse to quickly scroll the value inside