Wasps tend to build their nests in gaps, such as in between walls or in between fixtures. Nests are made out of dead wood and larvae of their young, which forms a pulp-like texture.
If there is a wasp's nest nearby, there will likely be a distinct increase in wasps in the vicinity travelling to and from its entrance. To identify the source of the nest, watch where the wasps tend to populate.
Be careful to keep a safe distance, though, to prevent you from being stung.