Beat the eggs and milk in a bowl until well combined. Mix in the salmon, dill, salt and pepper. Heat the butter in a large, non-stick skillet set over medium heat. Pour in the eggs. As mixture begins to set, gently move a heatproof spatula across the bottom and sides of the skillet to form large, soft curds. Cook until the eggs are thick, but still moist, with no visible liquid egg remaining. Place a half bagel on each of 4 plates. Divide and top with the scrambled eggs. Top the eggs with a dollop of sour cream, garnish with a dill sprig and serve.