Was sure Ken was wrong on a certain point (4)
I believe the answer is:
knew
'was sure' is the definition.
(I've seen this in another clue)
'ken was wrong on a certain point' is the wordplay.
'was wrong' is an anagram indicator (I've seen 'is wrong' mean this).
'on' says to put letters next to each other.
'a certain point' becomes 'w' (West. I am not sure about the 'certain' bit.).
'ken' with letters rearranged gives 'kne'.
'kne'+'w'='KNEW'
Can you help me to learn more?
(Other definitions for knew that I've seen before include "Was familiar with" , "Was conscious of" , "Was cognisant or aware of" , "Was aware of the fact" , "Had learnt; sounds like modern" .)