Key question about king’s personal attendant (7)
I believe the answer is:
equerry
'personal attendant' is the definition.
(term for a royal attendant)
'key question about king's' is the wordplay.
I cannot quite understand how this works, but
'key' could be 'e' (I've seen this in other clues) and 'e' is found within the answer.
'question' could be 'qu' and 'qu' is located in the answer.
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is found in the answer.
This explanation may well be incorrect...
(Other definitions for equerry that I've seen before include "Royal aide" , "Attendant at palace" , "Military royal attendant" , "Sovereign's officer" , "Officer attending a royal family member" .)