Providing more information such as what operating system you’re using would have been helpful. You also didn’t say, so I’m assuming you’re asking for an individual software application.
On the Mac, the active application menu sits just to the right of the Apple menu. Click that and choose the About submenu item to display the About dialog, which lists the application version number and other information.
On most versions of Windows, you can click the Help menu item of the active application and choose the About submenu item to see the application version.
Someone else could answer this better than I. If you installed your application using a package management system, then you could use the query interface. If you installed from source, try the using the -V switch.