Recently it has been renamed into abdominojugular test or reflux.
Basically, when you press on the right upper quadrant (the liver) you are compressing the liver with its sinusoids and pushing blood up into the right atrium which is reflected by an elevated JVP.
The test is difficult to perform and interpret but when it's done in the right way it highly corresponds to the capillary wedge pressure as it reflects how far you have congestion in the systemic circulation.
In Kussmaul's sign
you also have elevated JVP, but this time it happens during inspiration and usually associated with constrictive pericarditis, so the mechanism here is improper filling of the right atrium rather than too much filling of the right atrium.