right on the top, just outside the top balljoint, on the flat top of the knuckle.
It helps if you rotate the camber shim so the maxumum amount of knuckle is exposed.
Also this helps relieve some of the stress on the ball joint.
You should also undo the steering tie rods before you do this.
the key is to strike it straight down and let the heavy hammer do the work.
You dont need a puller or to pry it apart, the hammer will work best.
I fought these suckers for hours with pry bars, pullers, anything you can think of, the sledge works best.
Also the ball joint press kit will do you no good until you have the knuckle off the truck