Trim the ends from the onions, then remove the peel. Cut crosswise into thick discs (about 1 inch thick). Use your hands to push the slices apart so that each ring is a single onion layer.
Combine the flour, salt, pepper, and spices in a bowl. Whisk the eggs and buttermilk together in a second bowl. Place the panko breadcrumbs in a third bowl.
Preheat your air fryer to 400°F.
Use a fork or clean hands to dip the onion rings into the flour mixture. Shake off any excess flour, then dip into the egg mixture. Shake off any excess egg mixture, then coat in the breadcrumbs.
Lay the coated onion rings in a single layer in the basket of the air fryer and cook at 400°F for 10–15 minutes. You may need to cook in batches.