You can take flight from Chengdu to Zhanjiang, but there is a few flights between Chengdu and Zhanzhou, you need to pay attention to its real date.
There is no direct flight from Zhanjiang to Nanchang. You can make s transfer at Guangzhou. You could find the schedule and price through the page of China Flight Schedule(https://www.travelchinaguide.com/china-flights/) .