When is the wolfberry/goji berry festival in Ningxia?

You must refer to Goji Cultural Festival. It will be held in Zhongni during Sep. 16th and 20th. At that time, all kinds of Goji and relevant products, including juice and fruit wine, would be displayed. Then you can have a look at them and buy some on the spot if you would like to.

How to get to ningxia from guangzhou by train?

NX is municipality, which covers many cities and towns. 
Generally, from Yinchuan, the capital city of NX, you can take the only one train to reach Guangzhou. The train is K1295/K1298.