Answer to Question 1
the expected result would be that the foam would be more stable with the addition of sugar because sugar retards the denaturation of the egg proteins and ties up the water in the foam; however, sugar will delay the formation of the foam if added too early.
Answer to Question 2
Results may vary, but the expected result would be that the foam would be more stable when cream of tartar is added. Cream of tartar decreases the pH and enhances the denaturation of the egg proteins; the acid prevents the bubbles from bursting when you stop beating.