To track down the file holding each config option set on your own system:
  git config --list --show-origin

Generally, there are three configs:
  * git config puts stuff in /.git/config by default
  * git config --global puts stuff in /.gitconfig
    * On Linux/macOS, this means ~/.gitconfig
    * On Windows, this means %HOMEDRIVE%%HOMEPATH%\.gitconfig
      (not %USERPROFILE%\.gitconfig; these are not always the same)
  * git config --system puts stuff in a global config file shared by all users
    * On Linux, it's /etc/gitconfig
    * On macOS, it's /Applications/Xcode.app/Contents/Developer/usr/etc/gitconfig
    * On Windows, it's /etc/gitconfig