If you want to enable USB debugging on Android, just need to go to Settings > USB utilities > Connect storage to PC > Plug your USB to PC.

How do I enable USB debugging when my phone is broken?

If you want to enable USB debugging on Android, just need to go to Settings > USB utilities > Connect storage to PC > Plug your USB to PC.

How can I access my broken phone screen on my computer?

You need to pick a USB cable and connect your phone with PC. Go to AirDroid Cast on PC, click on the USB option, select your device from available list, start casting. After a successful connection, you can see your broken Android screen on PC.