I have a diabetic dog,I will be using two types of herb to help lower his sugar,the herbs are BITTERMELON and GYMNEMASYLVESTRE what I need to know is how much to give a 40lb dog

Proabably best to ask your vet I'm afraid.
We can't really give you an accurate dosage over the internet without physically seeing the dog, plus your vet may want to do some additional tests or give you some better alternatives :)

Without knowing the strength or form of these herbs you are giving, we cannot give you advice on how much to give.

This should be something you should discuss with your vet - he will be your first line of defense, and should be the first person you should go to when dealing with diabetes, as it is quite the learning process for owners.