Two colloquial readings to know. (1) Before a classifier,
哪 is often pronounced něi in casual northern speech — a fused form of
哪 +
一, parallel to
那 → nèi. So
哪个 becomes něige,
哪 +
本 becomes něi běn. Writing stays the same. (2) Sentence-finally after a word ending in -n,
哪 is a toneless emphatic particle — the n-coloured variant of
啊, as in
天哪 (good heavens) or
谢谢你哪 (thanks a lot). The exclamatory
哪 has nothing to do with which / where — it's just
啊 assimilated to the preceding -n.
