Mark engaging in a witty conversation (8)
I believe the answer is:
badinage
'witty conversation' is the definition.
(I've seen this before)
'mark engaging in a' is the wordplay.
'mark' becomes 'badge' (badging is a kind of marking**).
'engaging' indicates putting letters inside.
'in'+'a'='ina'
'badge' going around 'ina' is 'BADINAGE'.
(Other definitions for badinage that I've seen before include "Amiable banter" , "Frivolous banter" , "Chaff" , "Frivolous repartee" , "bit of playful repartee" .)