Quoting How To Take A Mac Screenshot Without A Keyboard

If your Mac keyboard is not working properly or is disconnected, to take a screenshot of your Mac, follow the steps below.

how to screenshot on mac ?

1. Open your Dock and click the Finder icon
2. Look at the Finder menu bar at the top of the screen. Choose Go > Applications
3. On the Applications page that opens, double-click the Utilities.
4. On the Utilities page that opens, double-click the Screenshot.