How to use the ground wire in 2 prong plugs
That cord is meant to plug into a Japanese outlet.  In Japan, it's common to have two-prong sockets with a separate grounding screw below for devices that need it.
The outlet it was desinged to plug into looks something like this:

To use your monitor in the US, simply replace that cord with a standard US computer monitor cord, an IEC C13 - NEMA 5.  They're very inexpensive.