One way you will know is if your efile rejects because someone already claimed you. But you won't know who. Then you can change it to say you are being claimed and resend it. Unless you really don't qualify to be claimed.
Do you need to check your return? If you (or your spouse) can be claimed as a dependent, check your return. On the 2019 1040 check the Standard Deduction section under your name and address. There is a checkbox if someone can claim you or your spouse.
That would not be checked if you are claiming yourself.