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