Karate student of 30 years - you cant. Knocking someone out requires striking the skull with sufficient force to bruise the brain. Brains have limited healing capacity.
The brain is two hemispheres of fatty tissue connected by a short but thick segment of the same kind of tissue. The two hemispheres float independently in the cerebrospinal fluid, so blows from many angles will cause a shearing effect on the connecting tissue. Even injuries that have no immediate symptoms (i.e. no knockout) can express decades later because the injuries can be deep in the brain. Memory impairment, loss of self control, inability to process emotional and social cues are some of the long term symptoms.