in the HBP dombledore is drinking some mind of poison with Harry.. do آپ know what that thing is?

The potion is called the Drink of Despair. Its effects are the same as the presence of a Dementor, apparently. Drinking the potion makes آپ live again the worst memories آپ may have. Besides, it seems to have a weakening side-effect on the body that ingests it.

In HBP, only Dumbledore drank of it. Harry was there to give it to him. He did not drink of it.