Wash the potatoes and cook in boiling water for about 20 minutes. In the meantime, peel and finely chop the onions. Wash the herbs and pat dry. Finely chop the parsley and dill, cut the chives into fine rolls. Mix the vinegar, lemon juice, salt, pepper and sugar together. Beat in the oil and add the herbs. Drain the potatoes, rinse in cold water and peel. Cut the potatoes into slices. Pour the herb vinaigrette over it and mix. Let the salad stand for about 30 minutes and serve with the salmon. Garnish with the rest of the parsley.