Possible Clues:

• End of an old riddle
• Riddle question
• End of many a riddle
• Riddle end, maybe
• End of a riddle
• Existential query, and a hint to the dish "chopped" around 16-, 20-, 38- and 54-Across
• Old riddle question
• Common riddle ending
• Question ending many a riddle
• Riddle-ending question