Listen, lady's possessing advanced knowledge (7)
I believe the answer is:
hearken
'listen' is the definition.
(hearkening is a kind of listening)
'lady's possessing advanced knowledge' is the wordplay.
'lady' becomes 'her' (her refers to a woman).
'possessing' means one lot of letters goes inside another.
'advanced' becomes 'a' (abbreviation).
'knowledge' becomes 'ken' (ken is a kind of knowledge).
'her' enclosing 'a' is 'hear'.
'hear'+'ken'='HEARKEN'
(Other definitions for hearken that I've seen before include "Listen in old way" , "Old attend" .)