Lazy-talk for "ask". Some individuals with abnormally large mouth parts and an unwillingness to learn and practice proper English pronunciations will intentionally utter this mispronunciation, because it's too much effort to generate the sound of a "k" immediately subsequent to the sound of an "s". And now, since it's accepted and not questioned, why bother?
SFN 1: Well, nigga, why dontcha aks him?!
SFN 2: You mean kill him?
SFN 1: No, dummass, aks him!
SFN 2: What the fuck! I'm not gonna axe him!
SFN 1: Sheeit, you ain't gonna find out where the shit is then!
SFN 2: If I axe him, I sure as fuck won't!
SFN 1: Get the fuck out...I'll aks him!