Know how to put in anagram of ear in cryptic (6)
I believe the answer is:
arcane
'cryptic' is the definition.
(I've seen this in another clue)
'know how to put in anagram of ear' is the wordplay.
'know how to' becomes 'can' (I've seen this in another clue).
'put in' means one lot of letters goes inside another.
'anagram of' indicates anagramming the letters.
'ear' with letters rearranged gives 'are'.
'can' placed into 'are' is 'ARCANE'.
'in' acts as a link.
(Other definitions for arcane that I've seen before include "Mysterious, secret or obscure" , "Requiring special knowledge" , "Mysterious, understood by few" , "Mysterious like a crane" , "Requiring secret or mysterious knowledge" .)