For Stunky, you'll need to find a female Team Rocket Grunt that specializes in Dark-type Pokémon, spouting these wise words: “Wherever there is light, there is also a shadow.” For Snover, the male Team Rocket Grunt is proficient in the Ice-type and will say “You're gonna be frozen in your tracks.”
Who has the shadow Snover?
As of right now, only female Team GO Rocket members will have Shadow Stunky or Shadow Snover in their team. Before starting the battle, you'll want to pay attention to the line of dialogue that appears on the screen before you choose your Pokemon.
How do I get shadow Snover?
Look for the grunt that says you are going to be frozen in your tracks. If a certain grunt says that, there is a big chance that it is a Shadow Snover. If the first Pokemon is a Snover, then you'll get an easy chance to catch a Shadow Snover after defeating the grunt.