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