Ms Trump exposed rising European villain (5)
I believe the answer is:
'villain' is the definition.
(I know that knave is a type of villain)
'ms trump exposed rising european' is the wordplay.
'ms' becomes 'k' (I can't justify this - if you can you should believe this answer much more).
'trump' becomes 'Ivana' (Ivana Trump, ex-wife of Donald Trump).
'exposed' means to look at the middle letters (outside letters removed).
'rising' says the letters should be written in reverse (going up in a down clue).
'european' becomes 'E' (abbreviation e.g. EU).
The centre of 'ivana' is 'van'.
'van' back-to-front is 'nav'.
Can you help me to learn more?
(Other definitions for knave that I've seen before include "[COURT CARD] , maybe" , "Jack (in playing cards)" , "A swindler" , "Jack in a pack of cards" , "cheat of old" .)