Whatever Zoro learns, his Next Main Fight makes that Lesson Obsolete,
King Fight already focused on Zoro's need for Haoshoku Haki, so his Next Fight was always meant to be Someone who cannot be Killed by it,
That's who Super Sommers is, (It's not like Oda created this Fight just so that Zoro repeats what Gaban already done)
Holy Knights are an Extension of Imu, so technically Zoro & Sanji are fighting Imu,
Zoro's Power Up needs to be something directly tied to countering Imu, not just countering Sommers,
It's like the challenge here, how do you Kill someone who is kept Alive by someone else you're not Fighting?
Zoro must severe their Connection, meaning his Actual Target is that Omen Ring, not Sommers who was already Defeated Twice,
Imu said that Omen stems from Envy, so I think counter to that is Opposite of Envy which is Admiration,
If Envy is a bad feeling for what others have, then Opposite is feeling happy for them, and that's literally what Zoro shown last Chapter,
He was clearly glad for the qualities that Sanji have, and believes his Victory is Guaranteed,
Zoro's New Lesson should be a Power that celebrates the success of others,
Seeing how Zoro & Sanji Fights gonna Parallel each other, and seeing how Sanji's Scene with Gaban happened after He heard Zoro have CoC,
I believe that just like Sanji is learning something Zoro already have (Haoshoku Haki), then Zoro will learn something Sanji already have,
I think that's his Flames,
In other words, Counter to Omen is Flaming Haoshoku Haki, it's just that each of Zoro & Sanji currently have different Half of that.
Zoro simply needs to upgrade his Fox-Fire Style & combine it with his Haoshoku Haki.
