Jacks (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">jacks</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know this)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for knaves that I've seen before include "Four face cards bearing a picture of a young prince" , "Jacks (cards)" , "Loons" , "Scoundrels" .)