Learn English – Term for a person who disagrees but says the same thing

Dysgraphia, per Dorland's Illustrated Medical Dictionary 31st Ed., is simply "difficulty in writing." Therefore, I disagree that this is a correct answer.

Agraphia is defined as:

"Impairment or loss of the ability to write; it takes two forms, one involving poor morphology of written letter forms and the other a reflection of the aphasia also observed in spoken language... Called also graphomotor aphasia"

I do think you need to carefully make a distinction between the person who never learned to write and those who have lost the ability to write. One may be a learning issue, whereas the other can be the result of a neurologic problem, such as a stroke. Agraphia and dysgraphia are terms that imply that the ability was once there, but is now either impaired or lost.

I don't know of a term that would cover the loss of the ability to write through disuse.

They are very likely informally termed tautonyms or as the Wikipedia page tells me, linguistically called reduplicants. There's a page full of people with reduplicated names including:

• José José
• Justo Justo
• Kelly Kelly
• Lisa Lisa
• Thomas T. Thomas

The term is not used solely for names with reduplicated first and last names, but also for other variants such as Jar Jar Binks or Richie Rich.