How do you get Defog in Pokemon Diamond Pearl?

Answer 1

Once you get defog, you teach it to a flying type Pokemon [or any Pokemon capable of learning defog]. When you are somewhere foggy, use defog and you can see where you are going. It's very helpful.

Answer 2

In Pastoria, you have to go to the Safari Zone. There you go inside, meaning into the Great Marsh. Just as you walk in, there are two people walking around. Go to the one with green hair on your right and talk to him. He has it and will give it to you.

Answer 3

you can get it by talking to the boy near the entrance of the greatmash