Content of quite a challenging lecture (5)
I believe the answer is:
teach
'lecture' is the definition.
(I know that lecture is a more specific form of teach)
'content of quite a challenging' is the wordplay.
'content of' indicates the answer is hidden within the clue.
'TEACH' can be found hidden inside 'quite a challenging'.
(Other definitions for teach that I've seen before include "Work with pupils" , "Work in school" , "Convey knowledge to students" , "Impart skills or 3 down" , "Impart knowledge" .)