To start remote debugging with Content Services running directly in Tomcat (i.e. not using containers but running Content Services based on a ZIP installation), then make sure you start Tomcat in debug mode (similar to how we configured the CATALINA_OPTS variable in the container environment). For more information on a ZIP installation, see Install with zip.
See this StackOverflow article for more information about how to start Apache Tomcat in debug mode. This article also links to the official Tomcat development page, which is a good read.
Debug some source code
Debugging in a Tomcat environment is the same as in a Docker container environment, see Debug Source Code.