Start over ... It can be one of two things
If your recipe is Chinese, "superior soy sauce" is soy sauce sweetened with molasses. It is thick and dark and is usually used in marinades and stews or to coat roasts or BBQs for colour. It is not generally used as a condiment on its own. You should be able to find it in Asian markets, if not the ethnic section of your supermarket. I don't know what a substitute might be.
Also, ketjap manis is sometimes called Indonesian sweet soy sauce. It's widely available in supermarkets (with various spellings), but if you can't find it you can mix equal parts ordinary soy sauce and brown sugar and simmer until the sugar is dissolved.
Just to complicate things, I think there's also a Japanese and a Thai sweet soy sauce.