Research on adult onset attention deficit disorder?

Yes! Provided that you mean adhd first diagnosed in adulthood. The diagnosis depends in part on evidence of adhd by age 7. Problem is, it is (or at least 20 years ago was) mainly picked up in childhood if it was the hyperactive type. The large number of inattentive type kids were not picked up, so we have to ask about symptoms in childhood specifically. Much researck in adhd first diagnosed in adults.
Adult ADD. Technically there would not be adult onset add. Adhd by definition has an onset in childhood. You could of course have adult add, that was not recognized until adulthood. You could also have impaired attentional abilities, difficulty with task completion, impulsivity, etc for reason other than add.