What version of macOS was on the old Mac and what version is installed on the new Mac?
Perhaps you had setup FileVault disk encryption on the old Mac system and the new Mac wants the password in order to import your old information into the new macOS system during migration? This FileVault password should have been saved when you did the initial FileVault setup -- does that ring a bell? You might be able to get it if you know the password for the account that setup FileVault, but I'm not certain. Not sure if you can recover anything without knowing this FileVault password. Perhaps a visit to your local Apple store and ask them for help? Or call Apple support for the new MacBook Pro you just got??
Good luck...
-bob