Place milk in shallow bowl; place bread crumbs on shallow plate. Dip fish fillets in milk; coat with bread crumbs.
Heat oil in large nonstick skillet over medium-high heat until hot. Add fish; cook 6 to 10 minutes or until fish flakes easily with fork, turning once. Remove fish from skillet; place on plate. Drain and discard oil from skillet.
Spread butter on one side of each slice of bread; place 4 slices, buttered side down, on work surface. Top each with cheese slice and fish fillet. Top each with sauerkraut and salad dressing. Cover with remaining slices of bread, buttered side up.
Heat same large nonstick skillet over medium-low heat until hot. Add sandwiches; cook 6 to 8 minutes or until bread is browned and cheese is melted, turning once.