Theatre skill doubled energy in comic dialogue (8)
'comic dialogue' is the definition.
(I've seen this before)
'theatre skill doubled energy' is the wordplay.
'theatre' becomes 'rep' (I've seen this before).
'skill' becomes 'art' (I've seen this before).
'doubled' indicates the doubling of some letters.
'energy' becomes 'e' (physics symbol as in E=mc2).
'e' doubled is 'ee'.
'in' is the link.
(Other definitions for repartee that I've seen before include "Sparkling conversation", "Witty and rapid conversation", "Banter - pear tree (anag)", "that may sound funny", "Ready wit".)