Which

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Old English hwilc, from the Germanic bases of who and alike.

wiktionary

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From Middle English which, hwic, wilche, hwilch, whilk, hwilc, from Old English hwelċ(“which”), from Proto-Germanic *hwilīkaz(“what kind”, literally “like what”), derived from *hwaz, equivalent to who +‎ like. Cognates include Scots whilk(“which”), West Frisian hokker(“which”), Dutch welk(“which”), Low German welk(“which”), German welcher(“which”), Danish hvilken(“which”), Swedish vilken(“which”), Norwegian hvilken(“which”), Icelandic hvílíkur(“which”).

etymonline

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which (pron.)

Old English hwilc (West Saxon, Anglian), hwælc (Northumbrian) "which," short for hwi-lic "of what form," from Proto-Germanic *hwa-lik- (source also of Old Saxon hwilik, Old Norse hvelikr, Swedish vilken, Old Frisian hwelik, Middle Dutch wilk, Dutch welk, Old High German hwelich, German welch, Gothic hvileiks "which"), from *hwi- "who" (from PIE root *kwo-, stem of relative and interrogative pronouns) + *likan "body, form" (source also of Old English lic "body;" see like (adj.)). In Middle English used as a relative pronoun where Modern English would use who, as still in the Lord's Prayer. Old English also had parallel forms hwelc and hwylc, which disappeared 15c.