To view the version history of the file which is being opened/selected, click 
at the right part of the toolbar;
Or, select View --> Version History... from the top menu.
The Version pane with content of the latest version are opened at the right column of the eXo IDE window.
The version name is displayed in the title of the Version pane.
Note
If the selected/opened file is not versioned yet, the View Version History function will be disabled.
The file version is opened in the read-only mode so you cannot edit it.
If any files are opened, the Version pane of the previously opened file will be closed automatically.