I don't think I've ever seen him dunk in a game. What about during warmups or a workout? I googled it, and the only instance I found was a clip from the 2K20 video game. (This clip was on the NBA's website under Suns highlights.)

Even though Jerome isn't as athletic as most NBA/college players in some obvious ways (e.g. jumping, speed), he's sneaky good in that he gets the job done anyway. He has other types of athleticism, like hand-eye coordination and the mental part of the game (e.g. knowing how to move to get open). I think some people write him off at a glance because of this, and it probably does hurt his career (e.g. fans don't think he passes the eye test). I have seen him move in ways that look uncoordinated, but he still gets the job done. For example, someone linked an article about him yesterday that had this twitter video of him making a last-second shot. He doesn't look very athletic in his drive and barely gets off the floor as he jumps, but still gets the shot in: