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