You can clone with
HTTPS or Subversion.
Hacking DNF | Writing Python 2 3 compatible code
The DNF documentation is maintained as reStructuredText in the doc/ directory of the source tree. You can build it yourself with make doc or read it online:
Freenode's irc channel #yum is meant for discussions related to both Yum and DNF. Questions should be asked there, issues discussed. Remember: #yum is not a support channel and prior research is expected from the questioner.