how to get the 28 digit iCloud code

If you’re referring to a 28 digit AppleID account recovery code (see -> How to generate a recovery key - Apple Support) there is nowhere to “get” it from. As stated in that link, you needed to write it down and save it somewhere, or keep it stored in a password manager, or somewhere you could retrieve it when needed.

It is imperative, when using a account recovery code, that you record the code so you can get it when you need it. Without it, you won’t be able to recover your AppleID. Since enabling a recovery code also disables Apple’s online account recovery system, Apple support can do nothing to help.

From the document at the link posted above:

“Using a recovery key is more secure, but it means that you’re responsible for maintaining access to your trusted devices and your recovery key. If you lose both of these items, you could be locked out of your account permanently. With that in mind, it's important to keep your recovery key in a safe place. You might want to give a copy of your recovery key to a family member, or keep copies in more than one place. That way you always have your recovery key when you need it.”