What is the sudo password?

Apparently you have been miseducated to expect that you can run anything you want with superuser privilege just by prepending "sudo " to it.  This was never the original intent of the sudo utility (see the sudo(1) manpage), and neither end-users nor commercial software vendors (personal pet peeve!) should expect this.

TLXOS is very locked-down.  You can only run a handful of commands (e.g. reboot, shutdown, and the command to start the local configuration utility (tlxconfig)) via sudo without entering a password, and TLXOS completely lacks the ability to authenticate via password - no local account (including root) has a password, there is no console login prompt, and sshd does not accept password authentication.  Consequently there is no way that you can gain superuser access except via root login using an SSH key trust.

If you want to perform an operation with superuser privilege, please read https://help.thinlinx.com/knowledgebase.php?article=7.