How many times do you use the HM move Defog in Pokemon Diamond?

You can't use Defog in Pokemon Diamond.

Here's why:

* Defog was introduced in Generation IV (Pokemon Diamond and Pearl), but only as a TM. It wasn't an HM.

* HM moves were limited to a set number of moves, each with a specific purpose like cutting down trees or pushing boulders.

While you can teach Defog to Pokemon in Diamond using a TM, it's not an HM move.