In a medium bowl, whisk buttermilk, sour cream, mayonnaise, chives, lemon juice, salt and pepper. Stir in cucumber. Refrigerate.
Heat 2 tbsp of the oil in a large nonstick skillet over medium-high heat. Coat scallops in flour and add half to skillet; cook 2 minutes per side. Season with 1/8 tsp each of the salt and pepper. Remove to a plate. Add remaining 1 tbsp oil to skillet and cook remaining scallops. Season with remaining 1/8 tsp each salt and pepper. Remove to plate.
In the same skillet, add corn and cook until charred, about 3 minutes. Stir occasionally.
In a large bowl, toss greens, frisée and fennel with half the dressing. Add scallops and corn. Serve with remaining dressing.