How do I disable the screenshot sound?

Either disable system sound effects or, I am assuming you want to disable only the screen shot sound, move or rename /usr/share/sounds/freedesktop/stereo/camera-shutter.oga

sudo mv /usr/share/sounds/freedesktop/stereo/camera-shutter.oga /usr/share/sounds/freedesktop/stereo/camera-shutter-disabled.oga

Although I've not tested it, but it seems that /usr/share/sounds/freedesktop/stereo/screen-capture.oga is the sound you're talking about.

Try renaming or moving it.

Also, in the properties of screen-capture.oga it is said it has as target the file camera-shutter.oga. so, it is a link to the later. i guess touching any of these would eliminate the sound

1. Click on the sound icon at the upper right corner of the screen.
2. Now click on the sound setting.

3. Now click on sound effect

   Now mute sound from here.

4. You have done. No Screenshot sound from now onwards.