Board Thread:Support Requests - Getting Technical/@comment-27087424-20160101162052/@comment-5454372-20160101165142

Had to get a little creative to find it, but their one is located here.

In general, it should be MediaWiki:Oasis-comments-header.

Edit: for future reference, Special:AllMessages will bring up a list of all the MediaWiki pages that exist on Wikia.

I found the specific one you were looking for by going to the top and setting "Filter by customisation state" to "Modified" (since the vast majority of them on most wikis haven't been changed from their default state), and then doing a Ctrl-F search for some of the sample text in the header that you were looking for.