To know the supported tomcat version in FNCI V6 instance, please navigate to <Installed dir>\tomcat\lib\ folder. Search for 'tomcat-api.jar (Executable Jar file)' inside lib folder. Extract the jar file and open it.

Then open META-INF file and inside that you will be able to see 'MANIFEST.MF' file.
Open the MANIFEST.MF' file and you will be able to see the details for supported tomcat version.

Please note to extract the Jar file (tomcat-api.jar) to a location outside of FlexNet Code Insight while leaving the original file in place while checking for the tomcat version so that nothing happens to the original file.