My son plans to travel to China, already have Q visa, what he need if he find a job there?

Lina, your son needs to find an employer who is qualified for recruiting foreigners. Then his employer can assist him to apply for the work permit. After getting the work permit, he can try to apply for the Z type from local entry and exit management bureau located at no.155, Jiefangnanlu (South Jiefang Road). If the officers there ask him to get back to apply in the USA, then he needs get back to apply.