Mobile Device Version
The effort levels of a specific Pokémon can only be viewed if the last game that the Pokémon was moved from was Pokémon Legends: Arceus.
If you want to check a Pokémon’s effort levels in Pokémon HOME, you can do so by moving the Pokémon back and forth from Pokémon Legends: Arceus.
Nintendo Switch Version
The effort levels of a specific Pokémon can only be viewed while Pokémon HOME is connected to a linked Pokémon Legends: Arceus game.