What is the default su password for my MacBook Pro for a new laptop?

There is no default.

Usernames and Passwords are created by you.

What are you trying to do. If you are trying to use the sudo command in terminal the password is your computer admin user password.

What happens when you try to use your admin password?

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The password for sudo is not echoed, but as long as you are an Admin user, it should work fine.