Place 5 potatoes in a large pot and cover with salted water. Bring to a boil.
Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and rinse with cold water to cool.
Remove and discard potato skins. Slice the potatoes.
In a large bowl, whisk together 2 tablespoons of vinegar, 1/2 teaspoon of white sugar, and ground salt and black pepper to taste.
Add the sliced potatoes, 1 chopped onion, and 2 tablespoons of pickled chopped gherkin to the bowl.
Stir the salad dressing into the mixture.
Fold 3/4 of the hard-boiled egg wedges into the mixture.
Garnish with the remaining egg wedges and 2 tablespoons of chopped parsley.
Cover the bowl with plastic wrap and refrigerate for 1 hour before serving.