It asks you for the password of the root user of the database. Please note that this password is the same one we configured when you launched the machine so if you don't remember that one you won't be able to access the database. However there is an alternative way to solve this. Instead of using "mysql -u root", you can use "mysql -u bn_wordpress" and the password that is set in the wp-config.php file.
Note: Can you try this alternative way to obtain the random password that was configured for your application
You can also try to obtain the password from this file
sudo cat /opt/bitnami/var/log/pre-start.log
No, the first post mentions how to reset the password of a WordPress' user. The second one allows you grant admin privileges to a user in case you accidentally removed those permissions.