The Manage Jenkins >> About Jenkins page shows the current release of Jenkins on your system plus information about licenses for all components. The top of the display shows the release and version of Jenkins that is running.
The following information about your Jenkins cluster is also provided:
List of all third-party libraries used for this release of Jenkins, with links to licensing details about each library.
List of static resources that are installed.
List of installed plugins, each of which includes a link to the page that shows all third-party dependencies for each plugin with a link to licensing details about each library.
This video shares different methods to check the version of Jenkins being used.