Preferred method - Use Project Griffon's Extension version information (see screenshot below). If you haven't used Griffon yet (aka AEP Assurance) you should definitely look into using this tool for data validation and simulation. Getting Started with Project Griffon
You can see in the screenshot that Griffon will not only tell you what version of the extensions are installed, but it can compare that version to the latest published version of the extension, letting you know how far out of date your extension potentially is. There is also a column to let you know if the Launch UI version of the extension needs to be updated.