Add calorie on top of skimmed sweet drink (6)
I believe the answer is:
coffee
'drink' is the definition.
(coffee is a kind of drink)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for coffee that I've seen before include "Common stimulant" , "Popular bean drink, maybe instant" , "Hot drink" , "It may be white, black, decaf or latte" , "Drink from 19s" .)