How can I find the top users for a specific tag? For example, Java on Stack Overflow. I want to filter the "Users" tab by Java the tag.
You can hover over the tag, which opens the mouseover thingy. Bottom Right Option is Top Users.
Alternately, in the queue for questions (example) you have a link called Top Users - nestled between Improve Tag Wiki and Synonyms.
Both the other answers mention hovering over a tag to get a link to the top users of that tag. Those links were visible in the old UI, but are no longer there.
To get to the top user ranking for a tag:
Visit the page of the tag in question, either by clicking on it or navigating to /questions/tagged/example
Alternatively you can navigate directly to /tags/example/topusers