I can\'t find at all where npm has its global settings stored.
npm config get userconfig
C:\\Users\\Jack\\.npmrc
npm config get glo
Start with npm root -- it will show you the root folder for NPM packages for the current user.
Add -g and you get a global folder. Don't forget to substract node_modules.
Use npm config / npm config -g and check that it'd create you a new .npmrc / npmrc file for you.
Tested on Windows 10 Pro, NPM v.6.4.1:
C:\Users\%username%\AppData\Roaming\npm\etc\npmrc
C:\Users\%username%\.npmrc
C:\Program Files\nodejs\node_modules\npm\npmrc
References: