How is one suppose to know about all of these sites? Well, they can look them up in a directory. http://sites.asia.wiki.org/
You may notice that there are several directories. Of course they are federated too. Wiki.cafe should host a directory of featured sites. This is the directory of directories with further instructions on how to participate. http://sites.asia.wiki.org/
One large diagram shows all visible sites with arcs connect sites that share some reference to each other. Find a link to the full diagram in the caption below.
This is the network of sites that have shared pages. Visualization is best on a 4k display.
Screen shot of small portion of large display. Hover shows out/in-bound links in red/green. Drag rotates. site 
We've modified the d3 bundle example to render site to/from site as arcs. original
Commit showing 3 changed files with 23 additions and 12 deletions. github
A separate tool shows how pages themselves link to each other. See Title Network Browser