Board Thread:Support Requests - Getting Technical/@comment-30348850-20191118010243/@comment-9605025-20191118040549

That part of the template is taking advantage of Google's platform.js script; In particular, the embedded subscribe button feature (see here). To use it, you will need to import Google's JS script via your wiki's site JS. I am not sure if this is the best way of doing it but the YouTube Wiki uses the following line of JS to do so. If your wikis does not have custom JS enabled yet, you will need to and ask them to enable it. Once it has been enabled, then you will be able to add the above line to your wiki's site JS.

What the template does is put a placeholder element on the page that Google's script later finds and replaces with the actual subscribe button. The specifics of how to make a placeholder element should be on the documentation page I linked to earlier in this reply.

One thing to note is that this will not work when viewing on a mobile device (unless your force your device to use the desktop view). The reason is that site JS is not loaded when viewing on mobile.