I think the title is quite clear, but I’ll repeat it here, for indexing purposes…
Is there a way to display category on site index?
By the way, displaying the categories as a menu item is not really interesting at journal level. The info should be at:
Front page on site level
block level, when viewing journals, if there’s ever a list of them available there.
It makes little sense, IMHO, to show a link “categories” on a journal’s main navigation.