What you are training
When a monitor starts to ring, you have about two seconds to find the frequency and notch it, and a wrong guess makes it worse. A low boom around 125 to 250 Hz, a nasal ring around 1 kHz, a harsh bark around 2.5 kHz, a whistle above 5 kHz: each has a character you can learn to name instantly, which turns feedback from a panic into a routine. This drill plays a feedback ring at a hidden frequency over a stage bed and asks you to name the band. The answer shows the frequency and the descriptor most engineers use for it. Six rounds cover the rings that come up on every vocal wedge. It is the same skill as studio frequency identification, under pressure and with a room in the loop, and it is the one a live engineer uses most.
After this drill, the plan: Your first Live Sound sessions drill the 1 kHz and 2.5 kHz rings, the two most common vocal-wedge problems, until the notch is reflex.