It isn't so much a practice how to use the buttons type of deal, when operating CNC machines. Its knowing how to use the work offsets, setting cutter comps etc. A good CNC book can explain that to you. All the various controls are different in how they accomplish the same task.
If you know how to use say a Fanuc control, and then are put in front of say a Fadal control, you will be very lost.
What you really need is the operators manual for those various controls. And to be actually there at the machine.
Your best bet is to go to a community college or something that has those kinda machines to learn what you want to know.