Jumping catch w ball.
My Sheltie will catch ball on fly or 1 bounce jumping for it.
You might also try Flying Disk.
You have to be really careful with that because any time a dog comes down on just his hind legs, you're risking a bad knee injury.
I don't know that there are any specific exercises for *knees* on the ball. I use it mostly for core strength. Have the dog stand on the ball while you stabilize it. Bounce it a little bit. Rock it front to back and side to side. Pick one of the dog's feet up and have them balance on just three feet. Rotate feet (front feet and back feet). Pick up opposite feet (right front, left rear for example) and have the dog balance on just the two feet.
Sit to stands both on the floor and on the ball. Things like walking through ladders and over cavaletti.
Ummmm... with Luce I do range of motion stuff because she's got some significant arthritis in her knees.