Is this a conversion trainer for the single seater or a different operational variant for different missions?
Check the discussions in the last few pages, such as here:
J-20 5th Generation Fighter VII
The twin seater is definitely for UAV swarms and commanding loyal wingman units. J-20 is an air superiority fighter and not a ground striker or attack plane. It has no need to weapons officer and even if it were, it still has no need for weapons officer. Computers have taken over that role...
www.sinodefenceforum.com
I also discussed it in a past article last year
Basically, the most likely role is as an enhanced battle management fighter that includes UAV control capabilities.
Conversion trainers don't make sense for 5th gen aircraft given modern training syllabuses and LIFTs available.