As shown later in his career, he can be hurt and knocked out. Good luck catching him with a knockout blow in his prime though. Guy had super human reflexes in his prime and I believe only the best of the best could touch him. I would give a guy like a prime Michael Spinks a good shot at catching him with that right hand.
Put him back in the days of cruiser sized heavies like say 1958-1960 and have him be an opponent of prime Sonny Liston. Then observe what Liston does and wala, there you have it.
You would need a super awkward Maidana style fighter With power. Roy did duck a few of those in his prime. Benn and Dariusz Michalczewski could have done it.
Either have 1 punch knockout power and the ability to land that power (Foreman), or be a similar level of freakazoid speed and ring mastery as him (Charles)
His prime was a super middleweight and light heavyweight.I do not see anybody beating him at super middleweight.At lightheavweight, Charles or Spinks come to my mind who would beat him in my view
well the style which could work is with a jab.. That would get the opponent landing to set up the punches to land. If the opponent cannot land the jab he won't get off his other punches either.
In his prime, with considerable difficulty. The most obvious way is for a boxer-puncher to march in and attack with sophistication and finesse but also with a some abandon to not allow him time to think, control the distance, draw leads, set traps etc. That involves having a good chin though because you'd be bound to take some hard shots that you don't see coming. Jabbing below his neckline and being able to punch with him or at the same time seemingly worked for Griffin. Not being drawn into always getting off first. It's a risky approach though because of his speed and accuracy, and his feinting ability; you'd need to be cute defensively and very adept at reading his pattern of attack to carry it off successfully. Griffin's height or lack thereof helped him, but he didn't have the chin. An elite swarmer could do it, but how many of those have we seen at 160-175? Like, the best of the best? Jones was adept at dealing with most types of pressure, to a certain calibre of fighter at least. He's not the monster at 175 he was at 160 and 168 though. There are plenty of light heavy greats who wouldn't have shown the fat, ancient McCallum the excess of respect that Roy did, or be content to just potshot a smaller, older fighter in risk-averse fashion.
How about attacking to the body along with sustained pressure? You need to be extremely durable to do it, but it's not impossible. I'd pick HW version of Bob Fitzsimmons (who in reality was SMW) to beat him after a year of preparation. He would be able to study Jones, sparr with modern fighters with modern gloves and I think he'd be able to do that. With 1890s rules and gloves, Fitz would stop him quickly.