Question of identity (3)
I believe the answer is:
who
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">question of identity</span>' is the definition.<br/ ><span class="explanation-format__explanation">('who' is used to ask about someone's identity)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for who that I've seen before include "Question of identity" , "The - - , rock legends" , "Which people" , "medical experts" , "Doctor --, TV series" .)