Listen and learn, gaining knowledge (7)
I believe the answer is:
Here is my best explanation:
'listen' is the definition.
(hearkening is a kind of listening)
'learn gaining knowledge' is the wordplay.
'learn' becomes 'hear' (synonyms).
'gaining' says to put letters next to each other.
'knowledge' becomes 'ken' (ken is a kind of knowledge).
'and' is the link.