Top/center/forward on the intake manifold. If you're asking where it is... you probably haven't traced out and tested all the vacuum tubing for leaks. Nor tested the EGR valve itself by applying vacuum with a MityVac. Need to do all that first before replacing your existing valve (that might be fine) with a used one (that might be defective).
Gerry's in-famous top end rebuild thread will have photos and more details.