Does anyone have any information on the subject?
I read that the design was heavily influenced by the DC-2, which has NACA 2215/NACA 2209 (root/tip).
I found a picture showing the AT-2 airfoil, but I'm not sure if it's the same as the DC-2.
Thanks a lot Aeroweanie! Yes, it is probably indeed NACA 2215. I found another picture which is part of a newspaper article about the Nakajima factory in 1940. It shows the assembly of the AT-2s. You can also see a wing profile in the bottom centre of this one, though not in very good quality. It also looks like a NACA 2215.
Taking Shinpachi's information into account, the wingtip on the AT-2 may have been NACA 2409, the same as on the Northrop Gamma 2E.
By the way, a book about AT-2 was published in Japan, which is now very rare to find even in antiquarian bookshops and archives. I would be very curious to read it...