At the Pokemon league.
Around the vicinity of celadon city.
You have to train it up to level 40.
train it till its level 32 then it will evolve
find a place that has wild Pokemon the same level as it.
Seafoam Islands.
First of all you have to catch a cubone in the Lavender town memorial place. Then train it up to level 28 where it will evolve into Marowak!
In Pokemon Yellow (Game) your Cubone will evolve to a Marowak at level 28! Teach it and train it well, who knows? You just might be the next Pokemon leauge CHAMPION!
route 205 for Pokemon diamond, pearl and platinum. the trainers have Pokemon from level 10 to level 17
the only way is to get a charmander from red blue or yellow then train it to level 16 it will become charmeleon train it to level 36 and it becomes a charizard.
The best place to train Pokemon level 40 and above is at Mt. Silver. Since you cannot gain experience through multiplayer battling, the highest leveled place is Mt. Silver. Pokemon average level 40-49 in Mt. Silver, so it is a good place to train.
Pokemon league :P
elite 4