Completing the Team Go Rocket Special Research will reward you with a Super Rocket Radar, allowing you to find the boss, Giovanni. Beating Giovanni will net you a Legendary Shadow Pokémon.

As part of the quest, after beating all three Team Go Rocket leaders, you’ll get a Super Rocket Radar, allowing you to hunt down Giovanni. Just like the leaders, Giovanni will appear in Team Go ...

You will have to find Giovanni in the first place, too, which happens once you defeat enough Rocket Grunts to put together a Super Rocket Radar ... Gross Knot for both Pokemon's Fast Moves ...

Completing the Team Go Rocket Special Research will reward you with a Super Rocket Radar, allowing you to find the boss, Giovanni. Beating Giovanni will net you a Legendary Shadow Pokémon.