You do not have to do anything special to avail Jio offer on Moto Z2 Play. Just when you start using the mobile, insert your Jio sim and it will get activated by the Jio company itself.
Yes, Moto Z2 Play does have VoLTE support, also.
Moto Z2 Play has nano sized sim card slots.
Yes, Moto Z2 Play does support fast charging. It takes just 30 minutes to charge 50% battery. You can get about 8 hours of use by charging for just 15 minutes.
Yes, it does support OTG.