Build a level controlled oscillator with a resonant capacitor and inductor. Include a supply current meter. As the coil approaches the conductive EMI layer, the eddy currents induced in the conductive coating will draw power from the resonant circuit and be indicated by an increase in oscillator current.
EM waves will wrap around the outside of the conductive surface, so EMI coatings will only work if the lens is mounted in a metal wall or the end of a metal tube. The advantage of the conductive layer is probably in the reduction of static electricity attracting dust. Static can be eliminated without an EMI coating by using a drop of ethylene glycol, (antifreeze), when you wipe your lenses.