Sweet nob on the inside of sweets (6)
I believe the answer is:
toffee
'sweet' is the definition.
(toffee is a kind of sweet)
'nob on the inside of sweets' is the wordplay.
'nob' becomes 'toff' (synonyms).
'on the inside of' indicates the central letters (I've seen 'on the inside' mean this).
The central letters of 'sweets' are 'ee'.
'toff'+'ee'='TOFFEE'
(Other definitions for toffee that I've seen before include "Chewy sweet" , "Chewy confection" , "can we not do something for it?" , "Brittle confectionery" , "Sugar/butter sweet" .)