I have very little exposure to SonarQube but have been asked to make a document explaining how to set up / use "sonar-project.properties file". Any information or input would be greatly appreciated.
Here are some resources to get you started
https://www.wrightfully.com/setting-up-sonar-analysis-for-c-projects/ - See Step 6: The sonar-project.properties file.
https://docs.sonarqube.org/display/SCAN/Analyzing+with+SonarQube+Scanner
There are also some sample projects on github, you can refer to the project.properties files there as well, https://github.com/SonarSource/sonar-scanning-examples