We bought Ubuntu dedicated Server, I can't figure out where is my magento installed in our Ubuntu server. I am poor in CLI, Please help.
It's probably somewhere under /var/www, you can use this find command to look for Mage.php in all subdirectory's under /var/www
find /var/www -type f -name "Mage.php"
The apache configuration files will give you information on it's location, (if it runs Apache ofcourse). They can usually be found under /etc/apache2/sites-enabled and have a line something like this:
But, you could practically install magento anywhere you want if you configure it correctly. You can use above find command and and change the directory to for example /home in case it's installed in one of the users home directory.
I'm not sure if it's a smart move to go with a dedicated Ubuntu server if you're not known with it. Who's maintaining it? You should direct these questions to this person as it's server specific.