Can i test the glucose level after drinking coffee (no sugar or milk in it) ? and is it ok to drink coffee at morning before breakfast , and before my insulin and sagimet ?

You could test your sugar at anytime you want to, it is however important to put a note on your diary when the glucose was tested so that when it is reviewed it would be put in context. You could drink coffee and take your medications as per your clinician's instructions; like do not take insulin if you are not going to eat soon after to avoid hypoglycemia.

Yes, black coffee (no sugar, no cream) will not influence your blood glucose significantly, Ok to test after having coffee.