You only find out if you try to efile your return it rejects because you were claimed by someone else. But you can’t find out who claimed you. How old are you? Are you a full time student? You may qualify as a dependent.
If your return is rejecting you can print and mail it. And the IRS will determine if you can be a dependent. It may just be an honest mistake on someone else’s return (that you don’t even know). They might have accidentally typed a ssn wrong and got yours by mistake.