American can celebrate with an encore (4,4)
I believe the answer is:
sing sing
'american can' is the definition.
(Sing Sing is a US prison or 'can')
'celebrate with an encore' is the wordplay.
'celebrate' becomes 'sing' (I've seen this before).
'with an encore' shows that letters should be duplicated (an encore is a second performance).
'sing' duplicated is 'SING-SING'.
(Other definitions for sing sing that I've seen before include "New York state prison" , "NY prison" .)