What experiment can be done to determine the dependency of
photoelectric emission, from a photocell, on distance from away radiation?

Measure the electric current generated by the incident light. It'll
drop off with distance.

For quantitative results one might calibrate the Photo Cell by
measuring the current output versus the intensity of the incident
light. One should then be able to verify that the output current
of the Photo Cell varies as the inverse square of the distance of
the Photo Cell from the source as predicted by Einstein's theory
of the photoelectric effect which incidentally earned him
a Nobel prize in Physics (1921 maybe????).