The cook of the Straw Hat Pirates, Sanji is one of the main characters in the One Piece manga, joining the crew during the Baratie arc. Although his main job is cooking, Sanji isn't just a cook. He's an exceptionally powerful fighter who is capable of beating some of the most dangerous people in the One Piece world.
Sanji's skill is such that he ranks among the strongest of the Straw Hat Pirates, after Luffy and Zoro, in a group called the Monster Trio. During the timeskip, he improved both his cooking and his fighting skills.
8 Armament Haki
By training with the people of Momoiro Island, Sanji was able to tap into the skill of Armament Haki at some point during the timeskip. Unlike Luffy and Zoro, he didn't need to have this skill drilled into him. In fact, Sanji had no teacher during the timeskip. He had to fight his way through all adversities and get stronger.
In the process, Sanji awakened Armament Haki. Its usage was shown to the fans on several occasions after the timeskip. When Judge, Sanji's biological father, saw him capable of wielding Haki, he was surprised at how strong he'd become.
7 Observation Haki
Due to constantly being on the run in the fight against Ivankov and his people, Sanji managed to awaken Observation Haki as well. This is his strongest Haki type and in the Straw Hat Pirates, nobody can use its many applications as well as him, other than arguably Luffy.
Observation Haki allows Sanji to detect the presence of people and even sense their intent, power levels, and most importantly, true emotions. Sanji was able to tell Viola's true nature by just looking at her in the Dressrosa arc. In the Punk Hazard arc, Sanji heard the tear of a woman fall from miles away and came to her rescue immediately after.
6 Learned Conqueror's Haki
Sanji only has two types of Haki so far, however, he definitely has it in him to unlock Conqueror's Haki as well. Nonetheless, for now, Sanji doesn't have this power but certainly does know what it does.
After seeing Luffy use Conqueror's Haki on Fishman Island, Sanji was able to immediately tell what power he used, meaning he learned a great deal about it on Momoiro Island. Along with him, Zoro could also recognize the ability and he went on to gain it in the Wano Country arc.
5 Improve Diable Jambe
During the Enies Lobby arc, Sanji managed to tap into his latent powers and gain a power known as Diable Jambe. Simply put, this power allows Sanji to set his foot on fire by increasing its temperature, making his kicks faster and much more powerful. During the timeskip, Sanji trained his legs to become much stronger and gained the ability to set both of them on fire instead of just one.
What's more, Sanji's legs started to produce more fire and burned much hotter. When combined with Armament Haki, Sanji was even able to break a Pacifista's neck with ease, something that he couldn't do before the timeskip.
4 Hell Memories
The full potential of Sanji's Diable Jambe power was seen during the Fishman Island arc when he fought against Wadatsumi, a Wuton. After remembering the pain that he went through on Momoiro Island, Sanji's anger fuelled his flames even further and made him much more powerful.
In fact, Sanji's entire body was set on fire after remembering his hardships and using this power, he was able to defeat Wadatsumi in a single blow with Hell Memories. Evidently, Hell Memories becomes stronger the angrier Sanji is. On Onigashima, Sanji used it against Queen the Plague once again and sent even him flying without much trouble.
3 Sky Walk
Going back to Momoiro Island once again, Sanji was chased by the New Kamas and, in order to win his battle with them, he eventually started to fly instead of running using the Sky Walk. This technique is very similar to the CP9's Moon Walk but appears to be much faster.
After learning Sky Walk, Sanji made fighting aerially his forte, as mentioned by him during his fight against Judge. On Fishman Island, Sanji took down countless enemies from the Sky using Poele a Frire: Spectre from the sky.
2 Blue Walk
What mostly sets Sky Walk apart from Moon Walk is the fact that it can also be used underwater. Sanji calls this technique Blue Walk. It was first demonstrated by him on the way to Fishman Island. As noted by Usopp, Blue Walk makes Sanji move in the water like a Fishman, if not faster.
Not everybody can use this technique as competently as Sanji simply because the pressure underwater would crush them. Sanji was able to perform it at 5000 meters underwater, which was said to be enough to crush a submarine with ease.
1 Attack Cuisine
After Sanji won his battle against Ivankov and his people, he was taught the Attack Cuisine by him, as promised. Unlike any other food, Attack Cuisine makes those who eat it much stronger, as noted by Sanji himself.
These dishes are what made the inhabitants of Momoiro Island strong as they are. To strengthen the crew, Sanji had to win these abilities from Ivankov. By defeating 99 New Kama Kenpo masters and avoiding becoming one of them, Sanji effectively won his battle and learned everything about this power. So far, he's used two of the 99 recipes in the story.