How can I find the exact address of the railway stations that I have bookings for?

first you should make sure which station your train departs from in Guangzhou, the Guangzhou Railway Station or Guangzhou East Railway Station.
Guangzhou Railway Station is located at No.159 Huanshi West Road, Yuexiu District, and it can be reached by subway line 2 and 5. Guangzhou East Railway Station is located at No.1 Dongzhan Road, Tianhe District, and it can be reached by subway line 1 and 3 (north branch).

Nanning Railway Station is located at No.28 Zhonghua Road. There is broadcast telling you when to get off the train.

The last stop is Kunming Railway Station of the journey from Nanning to Kunming, so you just follow the rest of the passengers to leave.