Where to Find and Catch Watchog
From Pokemon Go Wiki
Watchog are found and captured in Nest and Habitat locations.
Nests
Watchog Nests are locations that consistently spawn Watchog.
Habitats
Watchog Habitats are spawn locations where Watchog is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: