Dash to squeal about affair (10)
I believe the answer is:
smattering
'dash' is the definition.
(I've seen this before)
'squeal about affair' is the wordplay.
'squeal' becomes 'sing' (both can mean to act as an informant).
'about' indicates putting letters inside.
'affair' becomes 'matter' (synonyms).
'sing' placed around 'matter' is 'SMATTERING'.
'to' is the link.
(Other definitions for smattering that I've seen before include "Taste" , "Little bit" , "bit of learning" , "superficial knowledge" , "Tiny amount (of knowledge)" .)