



Sanji is not only going to awaken his Conqueror's Haki but he is also going to awaken Observation Killing... Now hear me out. (My parlay prediction)
In Wano, it was shown that Zoro had/revealed Conqueror's Haki as well as being able to use Conqueror's Haki coating before Luffy used it. Sure at first he used it unconsciously and briefly before finally using it against King, and even in that fight he still didn't know he was using Conqueror's Haki coating but that does not change the fact that he used it before Luffy.
You can even say that his attack with Kaido serve as a hint on what was the next advance stage of Conqueror's Haki. At this point, the only stage left in Conqueror's Haki is Observation Haki which Shanks uses, since there is new level of Conqueror's Haki for the Holy Knight's immortality.
It's pretty much certain that Luffy will have to face/meet Shanks at one point during the following arcs and Shanks to this day is the only character that is known to use Observation Killing. For Luffy to become Pirate King he will need to surpass even Shanks and it wouldn't make sense for Luffy to Surpass Shanks without being able to use Observation Killing, like how he surpassed Katakuri by learning Future Sight, Luffy will surpass Shanks by learning Observation Killing.
This is why I believe Sanji is going to awaken Observation Killing during his fight with Killingham, he isn't going to master it or realize what he just awaken. Like how Zoro didn't know he was using Conqueror's Haki coating and believe he was just using regular Armament Haki but in a larger quantity due to Enma, Sanji is going to mistaken Observation Killing for the regular effects of Conqueror's Haki which is the stunning and knocking someone out (I am exagerating the comparison but that is to make my point clear).
This would work in great parallel with Sanji and Zoro being the wings of the future Pirate King (Luffy) because for a bird to rise further above (A.K.A fly or in Luffy's case reach his dream), its wings (Sanji/Zoro) have to go above it at first to carry it higher in the sky when they go down (like when they defeat enemies or obstacles in Luffy's way).