哪
nǎ · HSK 1
which
口 (mouth) + 那 (that) — mouth asks 'that which one?'
哪 splits into 口 (mouth, the question-asker) and 那 (nà, that). The mouth component marks it as a spoken question word, and 那 supplies the sound — nà shifts to nǎ for the interrogative 'which'.
哪 — mouth 口 + that 那
A phono-semantic compound. The mouth radical 口 signals a spoken word or question particle, while 那 (nà, 'that') supplies the sound. Originally a variant of 那, it later specialized as the interrogative 'which?' in Mandarin.