The person at the top of the queue works in a restaurant (4,6)
I believe the answer is:
head waiter
'queue works in a restaurant' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'the person at the top' is the wordplay.
'the person' becomes 'waiter' (I can't explain this - if you can you should give a lot more credence to this answer).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the top' becomes 'head' (head is a kind of top).
'waiter' put after 'head' is 'HEAD WAITER'.
'of the' is the link.
Can you help me to learn more?
(Another definition for head waiter that I've seen is " Who may serve".)