1. Use the Move Relearner. The Move Relearner is an NPC located in the Pokémon League building in Lilycove City. He will teach any Pokémon a move that it has forgotten, for a fee. The fee is 10,000 PokéDollars for the first move, and then increases by 10,000 PokéDollars for each additional move.
2. Use a Heart Scale. Heart Scales are rare items that can be found in various places in the game. When you use a Heart Scale on a Pokémon, it will learn a random move that it has forgotten.
Here are the steps on how to teach Dig to a Pokémon in Emerald using the Move Relearner:
1. Go to Lilycove City and enter the Pokémon League building.
2. Go to the counter on the left side of the room and talk to the Move Relearner.
3. Select the Pokémon that you want to learn Dig.
4. Select Dig from the list of moves that the Pokémon has forgotten.
5. Pay the fee of 10,000 PokéDollars.
6. The Pokémon will learn Dig.
Here are the steps on how to teach Dig to a Pokémon in Emerald using a Heart Scale:
1. Find a Heart Scale in the game.
2. Go to your party menu and select the Pokémon that you want to learn Dig.
3. Use the Heart Scale on the Pokémon.
4. The Pokémon will learn a random move that it has forgotten.
5. If the Pokémon did not learn Dig, you can repeat steps 2-4 until it does.