Subsequent to reaching a mining level of 350 and learning Grand Master Miner, you will be able to proceed in searching for Cobalt Ores in the game.
I recommend the Howling Fjord as a good location on where to mine in WoW for Cobalt Ore. This place can be found just southeast of Northrend.
To travel here as an Alliance member, you can ride a boat in the Wetlands which will connect Valgrade to Menethil Harbor. If you are a Horde member, you can ride a zeppelin in the Tirisfal Glades which would get you to the Undercity that connects to a town called Vengeance Landing.
Alternatively, you can find a lot of Cobalt Veins in the Borean Tundra which is located at the distant western region of Northrend.
- Your mining skill is at least 400 to farm effectively
Before moving on to the next zone.