Dr burned two moles off 6yr ago. no pathology. how would i know if there was a concern now re melanoma? what should i do now ?

Don't worry: If it was 6 years ago and there was no path done and the area looks fine i would see no reason to worry. If you have any other suspicious lesions have them checked out. Most doctors won't take off a mole without sending it to pathology unless they feel there is zero chance of it being worrisome.

Biopsy: The area of mole cauterization may have residual discoloration, and that area may be biopsied. If there is no further evidence, then there is no way to know.

Ablated nevi: If you don't have any growths in the scars that resulted from the ablation, its really unlikely you have anything to worry about. Ablation of moles does carry the risk of a delay in diagnosis of skin cancer but if you truly had something there, i would expect it to have showed itself by now. You do need to see your doctor if any growths or pigmentation develop.

Rely on experience: You must rely on the physicians experience or consider having the scar biopsied to see if there is any remaining melanocytes in the deep dermis of the scar. The burning itself could have treated the problem.