A book on Capone, a disreputable American (5)
I believe the answer is:
album
'a book' is the definition.
(album is a kind of book)
'on capone a disreputable american' is the wordplay.
'on' is a charade indicator (letters next to each other).
'capone' becomes 'Al' (gangster Al Capone).
'a disreputable american' becomes 'bum' (I am not sure about this - if you are sure you should believe this answer much more).
'al' next to 'bum' is 'ALBUM'.
Can you help me to learn more?
(Other definitions for album that I've seen before include "LP, perhaps?" , "Pictures" , "Recording; book" , "CD, say" , "Compilation of recordings" .)