It was stated by Luffy that Sanji possesses Haki, when discussing it in the context of members of his crew who could fight Caesar Clown, a Logia user. Since Law was referring to the ability to coat themselves in armor, it confirms Sanji as a Busoshoku Haki user. However, Sanji did not actively display any of these abilities until the Punk Hazard Arc when searching for Kin’emon’s body using Kenbunshoku Haki.
Although it is unknown if he can use it, Sanji does know about Haoshoku Haki, something he (along with the rest of the crew) had not shown any knowledge of during the first half of the series. He, along with Zoro, has commented on Luffy’s ability to passively knock out half of Hody’s men, noting that he actually possesses it. It was also hinted at during the Fishman Island Arc, that both he and Zoro possess Kenbunshoku Haki when asked by Luffy if the pair could sense a “wild animal” in the Ryugu Palace, which they both answered that they could.
Kenbunshoku Haki is Sanji’s speciality concerning Haki. When helping Kin’emon recover his torso from within the lake on Punk Hazard, Sanji actively used Kenbunshoku Haki in order to locate the samurai’s torso within the dark water. Sanji seems to be really proficent using this kind of Haki, as being able to perceive Tashigi being beaten by Vergo despite the long distance between them, detect a sniper at a 16 mts. rooftop and act before him, finding the Thousand Sunny (with some of their crewmates aboard) in the middle of the sea or even to tell people’s true intentions the first time they meet (as with Kin’emon or Viola). He was also able to sense Nekomamushi’s aura from within Capone Bege’s body during the Zou Arc.