This template has two problems: a script error is hiding the link to the documentation, and the link to Wikipedia should be `https:`, not `http:`.
Template talk:Trope
Is there a trick to get the Wikipedia link to appear? I see it works on 1-800-Missing but doesn't display on Absent-Minded Professor or a few others in Category:Pages with working Wikipedia tabs.
The work pages use the "work" template, not the "trope" template. Since a supermajority of tropes don't have Wikipedia pages, that function isn't supported in the "trope" template.
As for the documentation, it's appearing on my screen. (I use various versions of the Firefox browser depending on which computer I'm using.)
The doc complaint is three years old and has nothing to do with Carlb's comment. I suspect it's been fixed since then.
Tropes -- pages with the {{trope}} template as their first line -- don't normally get Wikipedia link tabs because they rarely have pages there. 1-800-Missing is a work, which Wikipedia does catalog.
Trope pages in that category are just sloppy work -- someone added a wppage parameter to {{trope}} but didn't look to see if it appeared on the page after. (It won't. If it's supported for the page type, it's always visible.) There are no tropes with working Wikipedia tabs.
That said, if you want to suggest that {{trope}} display Wikipedia tabs, bring it up as a suggestion in the Tech Wishlist and Bug Reports forum.