Looking up...
どの人が田中さんですか。
Which person is Mr. Tanaka?
Which person or who (used to single out one individual from a group of three or more)
写真の中で、どの人があなたの先生ですか。
In the photo, which person is your teacher?
Slightly more conversational and explicit than 誰 (dare).
While どの人 (dono hito) and 誰 (dare) are fine among friends or peers, always switch to どなた (donata) when asking politely about someone superior or unfamiliar.
Use どの (dono) or どの人 (dono hito) when selecting among three or more people. If choosing between only two people, use どちら (dochira) instead.
Combination of the pre-noun demonstrative どの (dono, 'which') and the noun 人 (hito, 'person').
Use どの人 when choosing one person out of a group of three or more. For polite or formal situations, use どなた (donata) or どちら様 (dochirasama) instead.