Where do KNS2-enabled applications get their data from? And where can the maintainers or users of these applications upload data to?
The development page gives you information on how to get an SVN account on that machine. Currently, new stuff can be added by you with this account, but every new repository must be installed by the administrator.
Technical information about repository maintenance can be found in the documentation on SVN-backed repositories which is currently the recommended repository choice.