Smoke from the car in which Joe is reversing? (5)
I believe the answer is:
cigar
'smoke' is the definition.
(smoke can mean a cigar)
'car in which joe is reversing?' is the wordplay.
'in which' is an insertion indicator.
'joe' becomes 'GI' (GI Joe).
'is reversing?' says the letters should be written in reverse.
'gi' written backwards gives 'ig'.
'car' going around 'ig' is 'CIGAR'.
'from the' acts as a link.
(Other definitions for cigar that I've seen before include "Eg, Havana, panatella" , "Tobacco product" , "Corona, eg" , "Eg, a cheroot" , "Smoked item" .)