Sorry for the delay! Local naturalists who are familiar with the parks they support become familiar with owls that nest and hunt their parks. In my area that is the Metro Parks. Or you may have an Audubon Society in your town/area that uses expert birder members who are also familiar with where and when owls typically are. You are never guaranteed to see an owl on an owl walk, but if you are in the right place at the right time there is usually a very good chance you will hear their calls. And your guide will know where to look to increase your chance of seeing one. I participated in an owl walk in the fall where we heard a lot of calls but no sightings, but it was still extremely cool. Then sometimes you get to see one and that is also cool.