I have no idea! (6,2)
I believe the answer is:
search me
'i have no idea' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for search me that I've seen before include "Who knows? 14 [NOT-I] !" , "what a customs officer may do" , "I certainly don't know" , "I don't know (colloq.)" , "I don't know, informally, about cashmere - frisk away" .)