The most reliable way to find out if your license is suspended is to call or visit your state Department of Motor Vehicles or equivalent government agency and ask them directly. Some states allow you to check the status of your license online.
Most states provide you with some sort of official notification before your license is suspended. This can take several forms. If your license is at risk of suspension because you have accumulated multiple minor traffic violations in a short time, you may be mailed a notice and have the opportunity to have a hearing before the suspension takes effect. If your suspension is due to a criminal act such as driving while intoxicated, the suspension is probably going to be announced during your arraignment or sentencing. Even if you do not receive any notification, the suspension is still valid.
If you think you are at risk of license suspension and have not received any notice, it is a good idea to call the DMV. State laws and processes vary, so asking directly is the safest course of action. There are also commercial record-check options. These allow you to pay a fee and have them check the status of your license directly. It is important to use a reputable company to make sure the results are accurate.