Are bellysinkers and doorknobs other names for a doughnut?

No, "bellysinkers" and "doorknobs" are not commonly recognized names for a doughnut. "Bellysinkers" typically refer to a type of fried dough or pastry, while "doorknobs" may refer to a specific style of doughnut in some regions, but is not widely used. The most common name for the sweet, fried treat is simply "doughnut" or "donut."