The holder utilizes a hexagonal hole in the Prusa i3 top Z-axis mount. It fits the hole and holds a USB light cable.
In my case, a USB cable attaches to a Raspberry PI running Octoprint. I use a simple USB light on the other side of the cable.
See also on GitHub https://github.com/seek-treasure/3d-prusa-light-holder
The author hasn't provided the model origin yet.