How can i add third party repositories?
Search engine: “How can i add third party repositories to Debian?”
Why there is sources.list.backup file but there is not sources.list file? Also, which file contain whonix repositories, i see only debian repositories in the ‘apt’ directory?
This page should answer your question on Whonix-apt-repo.
The page says that the whonix repositories must be in /etc/apt/sources.list.d/whonix.list or /etc/apt/sources.list but there are no such files.