How do I fetch a branch on someone else’s fork on GitHub? [duplicate]

$ git remote add theirusername git@github.com:theirusername/reponame.git
$ git fetch theirusername
$ git checkout -b mynamefortheirbranch theirusername/theirbranch

Note that there are multiple “correct” URIs you can use for the remote when you add it in the first step.

• git@github.com:theirusername/reponame.git is an SSH-based URI
• https://github.com/theirusername/reponame.git is an HTTP URI

Which one you prefer to use will depend on your situation. GitHub has a help article explaining the difference and helping you choose: Which remote URL should I use?