easy route 26 kanto johto
the elite 4
Mount silver, or the elite four (With exp share.)
it depends what level your Roselia is. if it is higher than 40 it would be good to train it at the elite 4 if it is below level 40 it is good to train it anywhere with a EXP share.
Nowhere.
The best spot to train hunter in is the Feldip Hills as it can support your hunting to level 45.
turn back cave, mt.stark
give beautifly exp share and take him/her to the elite four and train there.
In Pokemon Diamond, a very good place to go is North of the Fight Area. All of the many trainers have level 45-60 Pokemon.
All you have to do is train your Pokemon or have a Pokemon with a good ice move
mt.silver is a good place because it has lvl.50 pokemon there
A good place for a level 76 is in the Stronghold of Security. On the first level, go to the treasure room, take the south exit out of that room, then keep going until you get to a room with level 27 minotours. This is a great place to train. There are also level 11 wovles there if you know someone weaker.
The only good place to train is the elite four unfortunately.