Possible Clues:

• Texter's 'Beats me'
• Texter’s “Beats me”
• 'No clue,' for short
• 'No idea,' for short
• Brief "Beats me!"
• 'Not sure,' for short
• "Beats me," in textspeak
• [shrug emoji]
• Brief "You got me"
• "Beats me," briefly