There are lots of tools we use to identify the nanomaterials we put onto surfaces.
One technique is called Ultraviolet–visible spectroscopy, thats a really complicated way of saying we shine different colour light through our sample and see what colours of light our samples absorb the most. The colour of light the sample absorbs is very particular to the kind of material on the surface and how much of that material there is.
Similarly instead of light, we can shine x-rays at our surface (X-ray photoelectron spectroscopy) that gives us other information about our sample, it not only shows what elements are on the surface but also what other elements they are bounded to!
We can use Atomic force microscopy to “feel” whats on the surface.
There are so many techniques you can use, it all depends on what information you want about your sample. If you want to just check if you sample is there or not, a microscope is the easiest!