How old is your dog? Is he still a puppy?
What breed or mix breed is he?
How long have you owned him? Has he always licked you and nibbled on your beard and hair? Do you mind this or do you want him to not do this? How do you react when he does this? How does your reaction affect him? Does he nibble on your hands also, or just your beard and hair? Where are you when this happens? (you must not be standing up, since he most likely could not reach you to do this then).
Has he always chewed on about anything, or is this a new behavior? Does he do this only when you are gone (or not watching him)? Does he do this when you are home? Do you ever see him doing chewing on things? What is your reaction to him when he is chewing something? How does your reaction affect him?
Do you punish him for chewing if you did not catch him doing it? If so, how do you punish him?
Has he had any training?