It is a code(secret key) generated from Coinbase that you can get when enabling the 2FA/TOTP from your account. So you will need a Google authenticator installed on PC or on your phone and add the secret key to your Google authenticator. Make sure you have a backup copy of that.

It would be better to read the guide from the Coinbase pro help page below to know how to set up 2FA.

Read under TOTP
- https://help.coinbase.com/en/pro/getting-started/authentication-and-verification/how-do-i-set-up-2-factor-authentication

For SMS, you will only receive a text with a code for verification that you will need when adding SMS verification from your account.