Neither local elders nor the Watchtower Society has a process to determine whether particular individuals donate or not.
On the other hand local elders and the Watchtower Society does have a process in place to determine whether a particular congregation is donating or not by comparison with other congregations in the area or elsewhere. This is a statistic that is watched very closely inside Watchtower as an early warning of something going awry. Watchtower crunches these numbers every way you can imagine for a range of reasons including 1) whether something's going wrong with a congregation, a circuit, a circuit overseer, an internal Branch attendant charged with overseeing a particular geographical area, and 2) projecting future cash flows.