Instructions
Place Stunky at the front of your Pokemon lineup so he is the first Pokemon to enter battles. This ensures Stunky will gain experience from each battle.
Battle wild Pokemon and other Pokemon trainers to gain experience. Additionally, use the Rare Candy item to automatically grant Stunky a level.
Select Stunky on the Pokemon lineup menu to view the amount of experience he currently has. The amount of experience he needs to reach the next level is found under the heading "To Next Lvl." Additionally, during battle, Stunky's experience is shown as a bar underneath his health bar.
Gain enough experience with Stunky to reach level 34. He will then automatically evolve into Skuntank. Stunky will evolve at the same level in every Pokemon game he is in.