Pat the chicken breast pieces completely dry with paper towels first, since wet chicken won't hold the flour well. Toss the cubes into a zip-top bag with the flour, seal it, and shake until every piece is evenly dusted. This thin flour layer is what helps the egg wash cling properly in the next step.
Whisk the eggs and milk together in one shallow bowl, then mix the breadcrumbs with garlic powder, paprika, salt, and pepper in another. I keep one hand for the wet mixture and one hand for the dry mixture so I don't end up with clumpy fingers. It sounds fussy, but it genuinely saves time.
Dip each floured chicken piece into the egg mixture, letting the excess drip off, then press it firmly into the seasoned breadcrumbs. Press gently so the crumbs really stick to the surface instead of falling off in the basket. Place each finished nugget on a parchment-lined tray as you go.
Spray the air fryer basket lightly with cooking spray, then arrange the nuggets in a single layer without letting them touch. Spray the tops too, then air fry at 400°F for 7 to 9 minutes, flipping halfway through so both sides turn evenly golden. Cook in batches if needed rather than crowding the basket.
Use a meat thermometer to confirm the thickest nugget has reached 165°F internally before pulling them out. Let them rest for a minute or two on the tray so the coating sets and stays crunchy. Serve immediately while they're hot for the best texture.