Maybe not one-punch him but definitely wobble him. Khan has a history of getting wobbled by jabs, I think a good straight hand, maybe a good combo from Brook could be too much for Khan's soft chin.
A few fast combos from Khan to Brook's face may see those eye sockets burst again. People are under-estimating the fact that Brook has TWO damaged eye sockets. He might as well be called Humpty Dumpty. Any big banger he comes against is going to target those weak areas on him now.