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