Almost all Ground types can learn Dig. The levels they learn Dig at vary. Also, if you want a Pokemon to remember the move Dig after it forgets that move, go to a Move Tutor that helps you in return for two Tinymushrooms, 1 big mushroom, or a Heart Scale.
Trapinch can learn Dig by itself at level 29 in Pokemon X and Y. In Pokemon Omega Ruby and Alpha Sapphire, it can learn Dig at level 19.
Sandslash learns Dig at level 30 in Pokemon X and Y. In Pokemon Omega Ruby and Alpha Sapphire, it can learn Dig at level 33.
trapinch can learn dig on level 41 The move dig is a TM that you get from somewhere, you can teach is to any Pokemon that is able.
In Pokemon Ruby, Sapphire, and Emerald, Nincada can learn Dig at level 45. It can learn Dig at a earlier level by using TM 28.
In Pokemon FireRed and LeafGreen, Diglett can learn Dig at level 17, which is a nice and early level for a good move.
If you level it up to level 45 you will be able to let it learn dig, but remember you'll have to delete a move to learn it.
Sandshrew learns dig at level 30 in Pokemon Sapphire. The ability to naturally learn dig make Sandshrew a valuable Pokemon. Since he can learn dig itself you don't have to use the TM dig on it.
Dig is a TM, so you can teach it to it at any level.
sandshrew can eventually learn it at level 44
Trapinch learns Dig at level 41 in Pokemon Ruby, Sapphire, and Emerald.
In Pokemon X and Y, Sandslash can learn Dig at level 30. In Omega Ruby and Alpha Sapphire, the level required increased to level 33.
A trapinch will learn dig at level 41 and a nincada at level 45