I sold a vehicle to my nephew and in Carson city there is no smog check, however, he lives in Reno and there is a smog check of which both of us didn't realize.

Who is responsible to fix the car if the car does not pass inspection and needs to be fixed?

Also, can he just take the car to the DMV in Carson and get it registered there?

He can not register it in Carson unless he lives there. So if he moves and has a Carson address then he can register it there.

But since he lives in Reno, it has to meet the Reno requirements.

How was the car sold, was there a warranty, or was it sold "as is" this should be stated on the bill of sale. Was there any promise that he would have no trouble getting it licensed ?

Basically this is his problem if the car was sold "as is"