Totally my Opinion:
You don't really "practice" or "train" the hook grip. You just lift. At some point, you're going to be pulling on the bar, your legs and back or traps will be able to handle the load, but your grip will not. In that moment, you decide you want that next rep, and THATS WHEN you hook grip!
In that Do or Die instant, you "learn" to do it. Its hard to "feel it" until you are about to drop the bar. When dudes grab a light bar to Practice, they tend to get their hands too tight, and get the barbell too high into the palms of their hands. And sorta cock their wrists funny. You need your hands and wrists to "hang like ropes, " like your elbows and shoulders do in a deadlift.