Has Kaido the Conqueror's Haki

Has Ace mastered any haki skills?

Yes, Ace owned Haoshoku Haki.

According to Portgas D. Ace's article on the One Piece Wiki:

Although not depicted in the main storyline, it was revealed in a flashback that Ace Haoshoku owned Haki, over which he had no conscious control at the time. Ace first demonstrated the ability at the age of 10 when he knocked the Bluejam Pirates crew unconscious after a fit of rage (only Bluejam himself remained conscious when Haki was released and was a senior East Blue player at the time). Just as Luffy used his haki to take out a crowd of Kuja warriors, Ace used his haki to take out the attacking members of Bluejam's pirate crew.

Ace was first shown to know about this when, during the battle at Marineford, he saw Luffy unknowingly unleash his haki and say, "You too?" He has never been seen with Haki except in his childhood.

Ace unleashed Haoshoku Haki in chapter 587 ...

... and Bluejam's pirate crew after they were hit by Aces Haki.

He may have developed and mastered other types of haki as well, but they are not shown in the manga. After all, he was the 2nd division commander of the Whitebeard Pirates and had the power of D.

abhishah901

The one-time use of Haki the Conqueror is insufficient evidence of the existence of all three Haki skills, and rumors have spread that Haki’s childhood demonstration was conducted by Dragon, who lurked in the shadows to protect Luffy and shut him down save like he did against Smoker. Also, did he not show Haki, even if his life is in danger? This is unusual and difficult to understand.

Mirror of truth

It is only enough once, in fact every body has haki, which is also called willpower. It depends on whether you enable it or not. There are conditions when haki is activated. Once activated, you should train it hard to control and master it here for more information on haki

abhishah901

Then why didn't he use it on Smoker, Blackbeard, and Akainu?

Mirror of truth

for that you should ask another question, the answer to the question in the comment will not be good