To export the Navigation-Popups gadget, click on "Download" button, save the downloaded file, go to Special:Import on destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
* Navigation-Popups[ResourceLoader|dependencies=mediawiki.api,mediawiki.user,mediawiki.util,user.options,mediawiki.jqueryMsg|type=general]|Navigation-Popups.js|Navigation-Popups.css
You must have appropriate permissions on destination wiki (including the right to edit system messages) and import from file uploads must be enabled.