Does the Latin verb nosco come from Greek, or did the shared root (cf. γιγνώσκω) end up in Greek and Latin separately? According to Wiktionary, it seems to be the latter case, as the free dictionary traces the ancestry of nosco back to proto-Italic, not to Greek. This came as a surprise to me.
If indeed the two words evolved independently, then what would explain the shared stem vowel ō which comes from the PIE root *ǵneh₃-? Would the change have come from an ablaut early on and then ended up in the two languages?