pronoun
Interrogative pronoun used when choosing from three or more items. For two items, use どちら or どっち.
どれが一番好きですか。
Which one do you like best?
この中からどれを選
Which one will you choose from these?
interjection
Interjection used to prompt a decision, express hesitation, or encourage action. Often used when the speaker is thinking or urging someone.
どれ、やってみようか。
Well, shall I give it a try?
どれどれ、見せてごらん。
Now, now, let me have a look.
From the interrogative prefix ど (do-) combined with the nominalizer れ (re), forming a pronoun meaning 'which one'. The kanji 何れ is a jukujikun reading.