How to Measure a Black Hole's Charge

A black hole can emit real photons also, like take a charge black hole and wiggle it. What happens is it's electric field wiggles because you're moving the black hole  and it generates electromagnetic radiation from the outside of the event horizon. Anything with mass that you wiggle generates gravitational radiation. You don't have to know anything about what's going on inside past the event Horizon. But if something has charged, even if it's a black hole or something else, you can feel it from a distance.