Speed and time stop.
Jotaro use combat speed if im not wrong
Let’s find out who wins
(Btw Kenshiro will be able to see Star Platinum because of his ability to see a fighters spirit, and a stands are described as a physical manifestation of a fighting spirit.)
Striking Strength
One time, Kenshiro was able to break a skyscraper in half. The average skyscraper weighs around 222,500 tons, so Kenshiro’s fists are more powerful than 5 tons of TNT!
Now on to Jotaro, who was able to break a row of teeth that were harder than diamonds, which means Star Platinum can strike with a force of 3,000,000 tons!
Jotaro’s diamond feat is way more powerful than Kenshiro’s
Jotaro: 1 Kenshiro: 0
Lifting Strength
Kenshiro was able to lift a 200 ton rock for several miles, while Jotaro was able to lift DIO’s roadroller which was over 60 tons
Kenshiro’s lifting strength is on a whole other level than Jotaro's
Jotaro: 1 Kenshiro: 1
Speed
Kenshiro has shown to be able to knock flying bullets out of the air which would make his reaction time at least 250 mph, Star Platinum has also shown to catch bullets out of point-blank range, so they both have similar reaction times. Star Platinum is stated to be faster than light, while Kenshiro has no real speed feats
Jotaro: 2 Kenshiro: 1
Durability
When Kenshiro broke that skyscraper, it fell on him, and he just walked past it like it was nothing. Kenshiro has also shown touching lava, without any burns or pain. Star Platinum is virtually invincible unless attacked by a stand, so Kenshiro can’t actually hurt him, Jotaro, however he can. Jotaro was able to survive point-blank explosions, whilst left unconscious. Kenshiro’s durability level is way more higher than Jotaro’s
Jotaro: 2 Kenshiro: 2
Verdict
Kenshiro will only really need one hit, but since Star Platinum has been stated to be faster than light and fought Silver Chariot (who was near light-speed) it’s safe to say that Kenshiro will have a slim chance of getting past Star Platinum. Kenshiro also has Muso Tensei, which gives him full intangibility, so Star Platinum can’t stop time and phase through his body to crush his heart or brain. Eventually, it comes down to durability. Star Platinum will have trouble hurting Kenshiro, as he is unaffected by lava which is at least 2,000 degrees F, and just walked through a falling skyscraper. It wouldn’t be long before Jotaro got tricked by one of his mirage clones and Kenshiro would just go in for the kill