Emirates served up cocktail of citron, first liqueur (9)
I believe the answer is:
cointreau
'liqueur' is the definition.
(I've seen this before)
'emirates served up cocktail of citron first' is the wordplay.
'emirates' becomes 'uae' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'served up' is a reversal indicator.
'cocktail of' indicates an anagram (I've seen 'cocktail' mean this).
'first' means one lot of letters go next to another.
'uae' reversed gives 'eau'.
'citron' is an anagram of 'cointr'.
'eau' after 'cointr' is 'COINTREAU'.
Can you help me to learn more?
(Other definitions for cointreau that I've seen before include "A sweet orange-flavoured liqueur for cautioner" , "Alcoholic drink" , "Sweet orange-flavoured colourless liqueur" , "Orange liqueur" .)