To identify the model and/or firmware version of a YubiKey or Security Key you have, use YubiKey Manager. It will show you the model, firmware version, and serial number of your YubiKey. Keep in mind serial numbers are unique across all models of YubiKeys, with the exception of Security Keys, which do not have serial numbers.
If you have an older YubiKey you can identify it through this link.
If your YubiKey supports FIDO (FIDO U2F or FIDO2), you can verify its genuineness on https://www.yubico.com/genuine/.