How can I add categories in the statistics?
I want to see this:
Categories - Forums - Themes - Message - Online - Users
And is it possible to add the top user?
Can someone help me? Where can I see the hooks used?
I'm sorry but there is no hook to add it. You should copy the wpForo template's footer.php fie to your active theme's /wpforo/ folder and customize it. More info in the doc: https://wpforo.com/docs/root/forum-themes/theme-customization/
More info about wpForo template files: https://wpforo.com/docs/root/forum-themes/theme-files/