Where does “how've” come from?

how've (English) comes from English how, from Middle English how, from Old English hū, from Proto-Germanic hwō, from Proto-Indo-European *kʷís.

Ancestry of “how've”, step by step

StepLanguageWordMeaning
1EnglishhowTo what degree; In what manner; In what state
2Middle Englishhowhow
3Old Englishhūhow
4Proto-Germanichwōhow, with what, by what means; instrumental of...
5Proto-Indo-European*kʷís—
Every word from Proto-Indo-European *kʷís →