Man of knowledge (3)
I believe the answer is:
ken
I believe this clue is a double definition.
'man' is the first definition.
(short for Kenneth)
'knowledge' is the second definition.
(ken is a kind of knowledge)
'of' is the link.
(Other definitions for ken that I've seen before include "One's range of knowledge" , "Identify; -- Livingstone" , "Notice" , "Understanding - boy's name" , "Know; man's name" .)