first blow is to the wind pipe with the sharp of the knuckles and the second to both temples with both fists at the same time. This is done because the energy of a singular blow is partially absorbed by the deflection of the head. Striking from both sides doubles the force of a single blow and with nowhere for the head to deflect it transmits all the energy. I’m sure there is probably some additional trauma to the brain from 2 intersecting shock waves but I’ll leave that to engineers to explain.