This kind of crossword's too difficult? They haven't a notion (8)
I believe the answer is:
clueless
'this kind of crossword's too difficult? they haven't a notion' is the definition.
The definition suggests an adjective which matches the answer.
'this kind of crossword's too' is the wordplay.
'this' becomes 'clue' (the clue referring to itself!).
'kind of crossword's' becomes 'less' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'too' is a charade indicator (letters next to each other).
'clue'+'less'='CLUELESS'
Can you help me to learn more?
(Other definitions for clueless that I've seen before include "like a crossword setter getting stuck?" , "Ignorant; helpless" , "not like our solvers!" , "Totally uninformed about what's going on" , "such a crossword can't be solved!" .)