What specialist would you see to diagnose writing disability brought on by tbi?

Physiatrist first: In many but not all areas there are physiatrists--rehab physicians--who specialize in tbi. In other areas it might be a neurologist. You might also need neuropsychological testing. I would start at a tertiary referral center to see if there is a physiatrist who specializes in this.

Rehab Physician: A rehab specialist can help diagnose the problem and has access to speech/language pathologists, physical and occupational therapists. The different therapists can help to better define the problem and can also provide assistance in recovery.