This repo contains the NuGet.exe command line tool.
The NuGet Docs cover the NuGet command-line tool in more detail:
If you're having trouble with the NuGet.org Website, file a bug on the NuGet Gallery Issue Tracker.
If you're having trouble with the NuGet client tools (the Visual Studio extension, NuGet.exe command line tool, etc.), file a bug on NuGet Home.
Check out the contributing page to see the best places to log issues and start discussions. The NuGet Home repo provides an overview of the different NuGet projects available.