Where to Find and Catch Whismur
From Pokemon Go Wiki
Whismur are found and captured in Nest and Habitat locations.
Nests
Whismur Nests are locations that consistently spawn Whismur.
Habitats
Whismur Habitats are spawn locations where Whismur 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: