Make a frying batter of eggs, flour, 2 tbsp. water, and salt. Stir until smooth. Dip duck cubes into batter and fry, a few at a time, in deep fat heated to 350-360 degrees, until golden brown. Drain on paper towels; put into a warm dish. Make a hot sauce with boiling water, cider vinegar, and sugar;stir until sugar is dissolved. Make a smooth mixture of cornstarch and soy sauce with 1/4 cup cold water;stir into vinegar-sugar mixture. Cook, stirring, over low heat until thickened. Add the ginger root, stir well, heat, and pour over fried duck.