GetXP is an addon to help if you are leveling characters with friends. It allows you to see other characters' xp. However, this addon will only work with other people who have the addon installed, so you need to get your friends to install it in order to use the addon.
How to use:
This addon adds a /getxp command. Type /getxp query and then the name of the character. That is, /getxp query <name>. This will send a query to the user, and print the character's xp and level in the chat window. You can also type /getxp window <character name> to display the information in a window.