Middle English word kne comes from Proto-Indo-European *ǵónwih₁, and later Proto-Germanic *knewą (Knee.)

Detailed word origin of kne

Dictionary entry	Language	Definition
*ǵónwih₁	Proto-Indo-European (ine-pro)
*knewą	Proto-Germanic (gem-pro)	Knee.
cnēo	Old English (ang)
kne	Middle English (enm)	Knee.