That will load jquery from the official CDN. The double ‘//’ lets it work on both http and https, without throwing an insecure content error. Its common to do this when using CDNs. Instead of the CDN url, you could use the URL pointing to your copy wherever it is… ie: myothersite.com/js/jquery.min.js
I personally always use the CDN. I never modify the original library. This makes it easier to upgrade in the future.
It’s not my intention to load an different jQuery version. My goal is to disable jQuery, because this library is loaded from an dedicated part of the website, which is not created by the Yii2 application.