Zoro could literally get the last hit to slay kaidou but he'll most likely be the one who cuts kaidou which allows Luffy to defeat him.
Timeline of Zoro during Wano Raid
Zoro fights Kyoshiro or Smoothie, and shows all of his post timeskip training which means Asura.
Zoro the fights King who probably has a black blade or some special form of armament. He learns how to cut fire after battling King's flames. His haki blooms as a result but he barely defeats King and he's at death's door. Maybe he opens his eye. He definitely learns whatever King knows.
Zoro makes it to kaidou's location. Everyone hears that he defeated King. Kaidou can't believe it and maybe attacks the almost dead Zoro.
Luffy stops Kaidou, Zoro tells luffy to hold off Kaidou for a bit, he will cut him.
Zoro is taken back to his fight vs Daz Bonez, the breath of all things. Every substance has a breath. He can hear Kaidou's scales breathing. He's taken back to Mihawks words about black blades, and his master koushiro.
Zoro jumps or is catapulted into the sky. Kaidou fires Boro breath at Zoro but he cuts through it. And then the moment comes where Zoro cuts through Kaidou's scales, sending the dragon back to the earth. Luffy takes advantage of this and defeats Kaidou with a final blow.