Place chicken in a large bowl and pour in pickle juice. Cover and refrigerate for 30 minutes. Preheat air fryer to 340°F (170°C). Whisk milk and eggs together in a bowl until well combined. Mix flour, powdered sugar, paprika, salt, pepper, and garlic powder together in a separate bowl. Remove chicken from pickle juice and discard pickle juice. Coat chicken in egg mixture and then dip into flour mixture, ensuring chicken is completely coated. Shake off excess flour. Spray air fryer basket or rack (depending on model) with cooking oil. Place chicken side-by-side inside air fryer basket or rack, working in batches if needed, and lightly mist chicken with cooking spray oil. Cook chicken in the air fryer for 6 minutes. Flip chicken, lightly mist with additional cooking oil spray, and cook for 6 minutes more. Increase temperature of air fryer to 400°F (200°C) degrees and continue cooking until chicken is no longer pink in the center and is crispy on the outside, about 4 minutes more on each side. Carefully remove chicken from air fryer and serve on toasted buns with 2 pickle slices on each sandwich.