The gauge reading is with engine and fuel pump off (not running) and after sitting for some minutes. Mainly showing where the test point is, and you do need a special fitting. You remove the pulsation damper and install the fitting in its place.
The 19mm wrench is to support the fuel rail when loosening and tightening the fitting or damper.

 

Can't really see the where your connecting the fitting.

 

Its where the pulsation damper is located, or just follow the fuel line to it. The thing that has the 2 rubber hoses connecting to it is the egr. So the connection is right behind it and is where the fuel line connects to the fuel rail.