One method of finding features on top of features is:
In the layer attribute table create a new x and y (both fields type DOUBLE) and right click on each and calculate each geometry (x and y values or centroid values)
Create another type TEXT field called concat and and field calculate the x and y field values together
Next, summarize the concat field (right click it in attribute table and select summarize option and take all default settings). This will provide a count table of all overlapping features by xy concatenation.
Finally, join the result of the summarize table to the layer table by concat field. All values with count > 1 are coincident features.