I did it many times, and each time I forgot where it was.
Menu File → Preferences → Settings.
I get this:
I want to open file settings.json (editable JSON file) instead. How can I do that?
To open the User settings:
This image was taken in the VS Code online editor
Which, from the manual and depending on platform, is one of:
%APPDATA%\Code\User\settings.json
²$HOME/Library/Application\ Support/Code/User/settings.json
$HOME/.config/Code/User/settings.json
The Workspace settings will be in a {workspaceName}.code-workspace
file where you saved it, and the Folder settings will be in a .vscode
folder if and when it has been created.
Official page on User and Workspace Settings
As stated by sevencardz below, VS Code includes a button in the Settings UI gutter which can be used to switch between JSON and graphical view.
The workbench.settings.editor
option selects which of the settings files is opened by default when not using the above method, such as with the shortcut ⌘+, or through the application menu.
Footnotes
The aforementioned settings, User and Workspace. Remote settings will appear when using WSL.
By a test this maps to %APPDATA%\Roaming\Code\User\settings.json
, I am not sure by what logic.