Pretty much feed it once a week for life. Watch for obesity and back off if need be. Size wise, feed a meal about as thick as the snake is in the middle.
what others said; once a week for life is good. my guy goes off food during breeding season and has a strong preference for mice over rats, but otherwise he is usually a sure-fire eater for me.
Another vote for once a week.
Kings can be absolutely voracious feeders. They will sometimes eat until they get sick, so a consistent 7 day schedule of the proper sized prey is ideal.
Don’t let those puppy dog eyes fool you into an every 4 or 5 day schedule and a sausage instead of a snake.
Someone on here - @ashleyraeanne maybe? - suggested prey 10% the size of the snake, by weight. Once a week. It has served me well with my Mexican Black Kingsnake.