If you want to duplicate your GitHub repository so that you have two identical repositories on GitHub:
git clone [existing-github-repo-url]
git remote add duplicate [new-github-repo-url]
git push duplicate master
If you want to duplicate your GitHub repository so that you have two identical repositories on GitHub:
git clone [existing-github-repo-url]
git remote add duplicate [new-github-repo-url]
git push duplicate master