Precisely locate cask in filling tankard (8)
I believe the answer is:
pinpoint
'precisely locate' is the definition.
(I know that to pinpoint is to exactly locate)
'cask in filling tankard' is the wordplay.
'cask' becomes 'pin' (I've seen this in other clues).
'filling' is an insertion indicator.
'tankard' becomes 'pot' (pot of beer).
'in' going inside 'pot' is 'point'.
'pin'+'point'='PINPOINT'
(Other definitions for pinpoint that I've seen before include "Tiny dot; locate exactly" , "Find the position of" , "something sharp" , "Define precisely" , "Precisely indicate" .)