Possible Clues:

• With no understanding
• Living in oblivion? No idea!
• Completely at sea about what's going on
• Had no idea drunk sells cue
• Foolish crook sells cue
• Piece of evidence, not so great, leaves one bewildered
• Iconic 1995 comedy that coined the phrase 17-Down (which is also hidden in 12- and 20-Across)
• Had no idea this is one of those from Takeaway
• Knowing nothing
• Having no idea! Not like you, the solver!