About: Chengdu-Huanglong-Jiuzhaiguo-Guangzhou-Changsa- Zhangjiajie

For your route, the G-trains only exist between Guangzhou nd Chashang. For other places, you need to choose to take the planes and buses.
The the trains' timetable, it is suggested to search on https://www.travelchinaguide.com/china-trains/.
From Chengdu to Huanglong and JZG, you can choose to fly to reach. From JZG, you can find to Guangzhou. From GZ to Changsha, you can take the G-train. From Changsha to ZJJ, you need to take the buses from Changshan West Bus Station.