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