Owls are nocturnal creatures so they're rarely seen during the day. This can make them difficult to find, but wherever there are owls you're going to find poop. Identifying owl poop is easy if you know what you're looking for.
Look for white droppings. Owl poop consists mostly of a white wash, much like most bird poop. This whiteness is caused by uric acid and is thought to be like urine.
See the brown additions. The brown droppings are the owl's actual poop although they don't have much here. Most of what owls can't digest comes back in the form of pellets rather than poop.
Find what looks like a good roost. Under any good roosting spot you'll find owl poop. These can be good hunting spots as well as nesting areas.
Find pellets. Pellets are different from owl poop. They are small globs of fur or feathers. Pellets also contain the prey's skeleton; sometimes it can be put completely back together. Owls swallow their prey whole but they can't digest much of what they swallow. The bones, feathers or fur that don't get digested are regurgitated as pellets. Scientists study these pellets to understand what owls are eating.
Owls can't fly while they're regurgitating a pellet. They must land to do so. An owl must regurgitate a pellet before it eats anything new because the pellet they're preparing to expel partially blocks their digestive system. For that reason, when an owl regurgitates a pellet it usually means it's ready to eat again.