Cook berries with 1/4 cup sugar, the water, and lemon juice in a cast-iron skillet set over a campfire or on a medium grill, until thickened, 10 to 15 minutes.
Meanwhile, whisk together flour, baking powder, baking soda, 1/4 teaspoon salt, and remaining 2 tablespoons sugar. Add buttermilk and butter; stir until a moist dough forms.
Spoon 6 dollops of dough over fruit. Sprinkle cinnamon-sugar over dough.
Cover skillet tightly with parchment-lined foil. Cook until dumplings are set and tops are dry, about 20 minutes.