I recommend you take the following steps to determine the actual folder:

• Connect to your QNAP using SSH
• Change directory to /shares/CACHEDEV1_DATA/.qpkg
• Then, run the following command:
  
  find . -name AppConfig.xml
• server.properties should be in the same folder where AppConfig.xml is found. Since server.properties does not initially exist, you search for AppConfig.xml instead.

By the way, we do not recommend running Xeams inside a container because the network is virtualized, and every message coming into Xeams will appear to be coming from your QNAP's IP. This makes filtering inefficient.