Training Area Level 46 - 60: Level(Maple Story Meso) 45 - 60 Straw Practice Dummies from Mu Lung would be excellent and this is the one place where mobbing skills become extremely useful. There is a fast spawn here and there are lots of Straw target Dummies too.
Training Area Level 61 - 70: Level(Maplestory powerleveling) 61 - 70 Gryphons in Masteria would be a great training choice. Gryphons are large in numbers, spawn quickly and the map is big. The only bad thing is that there is a pit that you might fall into and if you do you will be sent back to the previous map.
Training Area Level 71 - 82: Level 71 - 82 Voodoos and Hoodoos from the Haunted House make the best training choice for not only White Knights, but any other class around this level. As this area is always packed with other maplers trying to train, the map is small and enclosed and there is a quick spawn, but the only bad thing is trying to find a free channel.
Training Area Level 83 - 100 in Maplestory: Level 83 - 100 Dual Ghost Pirates in Ludibrium. The bad thing about the map here though is that occasionally many hacking Dragon Knights come and steal the map from White Knights. Trying to train and many times the hacker will leave their Dragon Knights there to steal EXP for hours on end, and so sometimes trying to train here can be difficult.