A small drink; the head (6)
I believe the answer is:
I believe this is a double definition.
'a small drink' is the first definition.
(I've seen this before)
'the head' is the second definition.
(noggin is a kind of head)
(Other definitions for noggin that I've seen before include "Head - tot" , "Small amount of alcohol" , "Gill usually" , "Small amount of liquor" , "Small measure of liquid" .)