Possible Clues:

• What the puzzled have
• What the befuddled have
• 'Beats me!'
• 'Search me'
• "Dunno"
• How to interpret 20-, 38-, and 56-Across
• 'Haven't the foggiest'
• 'I'm stumped'
• "Haven't the foggiest"
• 'Don't ask me'