Slice the onion into 1/2 inch thick rounds and place into a bowl of water.
In a large, ziploc bag, shake together the panko, garlic powder, salt, paprika and onion powder. Spread it into a shallow, rimmed plate. Place the egg into a small bowl and whisk together with the milk. Finally, spread the flour into a separate shallow, rimmed plate.
Remove an onion ring from the water, shaking it dry. Dredge it in the flour until coated, then into the egg, shaking off the excess. Use your dry hand to dip into into the panko, covering it well. Place the ring into the mesh basket of your air fryer and repeat with the onions until the basket is filled, but some room remains around each ring.
Cook at 400 degrees until golden brown and crispy, about 8-12 minutes. Keep them warm in a 200 degree oven while you repeat with the rest of the things - I needed to do about 3 batches for the whole onion.