This looks to take the newer style knee bar - when you look into the hole, is there a slot the end of the bar would slip into? There are two styles and this one is easier and cheaper to get.
Your machine will work fine if you disconnect the wires to the controler in the case, and use a double end plug on it. And a new foot pedal/cord plug set may be cheaper than the knee pedal, and for sure way easier to find. Otherised you need the single cord plug that only goes into the wall outlet.
BTW - if you decide to go that route (double cord plug) I'd love to buy the controller that is in the case. I have a case and knee bar, but the controller was busted up and non -functioning.