I don't know, but I would suspect that doing the knee reflex thing with someone asleep would often cause them to wake up?

But, also, I think I heard that the signal doesn't get all the way up to the brain before the signal to kick or whatever starts going down? (I am unsure of this though.)

So, I would think that the brain being like it is when the person is asleep wouldn't stop the kick reflex thing, because the brain isn't even what causes the kick reflex thing?

So my guess is that they would kick and then likely wake up.

I'm not certain of this though. Please correct me if I am wrong.