The location of the MySQL database files of XAMPP for Linux is /opt/lampp/var/mysql/
. But I think you don't need this information.
In your case you made a SQL dump of your databases. You only need to restore the dump the "usual" way on your Linux system: One way is to use phpMyAdmin and another way is to use the MySQL command line tool (/opt/lampp/bin/mysql).
For example: http://www.devshed.com/c/a/MySQL/Backin ... -Database/
Please prepend always /opt/lampp/bin/ to a MySQL command. For example if a tutorial says call mysql ...
you've to type /opt/lampp/bin/mysql ...
Hope this helps.
With many greetings from Germany