Heat oven to 400° F. Bake the salmon on a rimmed baking sheet until opaque throughout, 10 to 12 minutes. Let cool, then flake into large pieces.
Meanwhile, heat the oil in a large nonstick skillet over medium-high heat. Add the potatoes, onion, ½ teaspoon salt, and ¼ teaspoon pepper and cook, stirring occasionally, until the potatoes are tender, 8 to 10 minutes. Add the cabbage and caraway seeds and cook, stirring occasionally, until the cabbage is tender, 2 to 4 minutes. Stir in the salmon and cook until warmed through, 30 seconds. Stir in the vinegar. Serve warm.