As one who has written all his life:
First question you need to settle is, "How involved with d/Deaf people is your character and how does it effect them."
If the answer is "None" then this forum may not be useful to you.
If the answer is "A lot" then you need to learn FSL (French Sign Language) and become involved in the local Deaf community.
This is not really the type of subject you can book research.
