Title Suggestion: Where can I find PUK code on my iPhone?

You will need to contact your cell provider.

Do not enter the wrong PUK code too many times or you will destroy your SIM card. If that happens you will need to purchase another one from your carrier.

If you do not have it you need contact your provider. Here are AT&T instructions

https://www.att.com/support/article/wireless/KM1011771/

You don’t

Contact your cellular provider