Pokopia is not a real game title I can verify
If you mean a Nintendo Switch game, gamesharing is limited by Nintendo account rules
Buy the game on one Nintendo Account
Sign that account in on the other Switch
Set that Switch as the primary console for that account
Download the game on the primary console
On the secondary console, use the purchasing account to access the game
Keep the purchasing account signed in on the secondary console
Expect only one active player at a time for most digital games
If you mean a physical cartridge, lend the cartridge to the other person
If you want exact steps, tell me the platform and the exact game title