Questioned about suspicious rebel as seeing such a jacket (6-8)

'such a jacket' is the definition.
(double-breasted jacket is a type of jacket)

'questioned about suspicious rebel as' is the wordplay.
'questioned' becomes 'doubted' (doubting is a kind of questioning).
'about' indicates putting letters inside.
'suspicious' is an anagram indicator (an unusual or suspect spelling).
'rebel'+'as'='rebelas'
'rebelas' anagrammed gives 'lebreas'.
'doubted' placed around 'lebreas' is 'DOUBLE-BREASTED'.

'seeing' acts as a link.