Guys like Jacobs and Lemieux, if they caught him clean with a couple of big ones, might do the job. There's a reason why Golovkin fought a tactical fight from behind his jab.
Lemiuex could, if G wasnt so skilled and or chose to fight stupidly... but Gs good enough to neutralize much of his power with skill and fight him tactically.
Lemmy probably could, the dude has dynamite in his hands. Maybe if Lee was a little more active he could too.
Jacobs is the only one that can KO ggg... he is fast, powerful and bigger than ggg. Let's see if he can get to ggg in the rematch... charlo needs to prove himself at MW... let's see if his power carried up a weight class