Follow up:
Here is the respose I received from PADI Japan:
Hello,
Thank you for your email.
I'm not sure what "OKINAWA test" means, but probably it might be a national license called "Sensui-shi".
Regardless of nationality, a diving professional who wish to work in Japan needs to have this license. And especially in OKINAWA, the regulation is applied so strictly that you will be asked for your being qualified as "Sensui-shi" by employer or a police.
For more information on this regulation, please contact The OKINAWA Marine leisure Safety Bureau foundation(OMSB).
support@omsb.jp
Hope this helps.
Kind regards,