Trace your last name
There are numerous online resources available to help you learn more about the origins of your surname. If you have a paternal connection to your Jewish roots, this may be useful. If you have a common surname, this may not be as useful, but it can still tell you whether you are Jewish or not.
As an example, consider Ancestry.com's surname search tools. It lists information ranging from the expected lifespan of someone with your last name to common occupations, in addition to providing possible origins for your name. You can even find complete profiles with information about people who share the same name.