Re: How to focus 85mm 1.2 II properly ?
The 85mm 1.2 is a notoriously difficult lens to use at its largest aperture - if you're really critical about sharpness, expect most images to be slightly out of focus.
AF microadjustment would be my first stop, just to rule that out.
The rest is mostly about technique, as others have pointed out.
Still, it's difficult. Some of the above posters that are downplaying the difficulty level can't be very critical about sharpness at 1:1, as perfectly focused images ARE elusive. But usually worth the effort.
Servo, burst, spot focus point on the eye, no recomposing should give better results.
The most foolproof technique if the situation allows for it is to put your camera on a tripod and do live view, zoom in on the models eye on the display and do manual focus. The optical viewfinder in itself will not allow for precise enough manual focus with this lens. You need magnification to really see what you're doing (I have perfect vision and still can't tell when the image is 100% properly focused by just looking through the viewfinder. It's not a matter of eyesight, but rather of giving your eye sufficient info to work with to really tell the difference between a 95% focussed image and a 100% focused image).
I wouldn't use this lens at 1.2 for events, it's simply not an action lens. The AF on this lens is so slow that I would prefer almost any other L zoom covering the same field of view to the 85mm 1.2 for action. Or save a ton of money and buy/use the 85 f1.8 instead, its focussing faster. As others have pointed out, the 1.2 is a specialized portrait lens, and should be treated as such.