For different needs. On most surfaces you use a really fine brush, like a womans face powder brush, to gently dust the area where you think there are prints and the powder sticks to the whorls of the print. Then you lay a piece of clear tape over it and peel it off with the print. Or take good close-up photos. Different coloured powders for different coloured surfaces too so you can see the prints better.
Put a big thumbprint on the screen of your phone, dust with talcum powder then shake/blow off the excess. Ta da!
You'll see it better if the screen is dark. I have some super fine decolourizing charcoal that would probably work great.