Hi Junaid,
As Hiko_Davis advised you need to remove the first section of your command which uses the java command and leave the last part which should use the jar command (not tar command)
/opt/CA/APM/10.5.2.24/jre/bin/java -Xmx128M tar -tvf /opt/CA/APM/10.5.2.24/config/modules/jun/Supportability.jar
->
jar -tvf /opt/CA/APM/10.5.2.24/config/modules/jun/Supportability.jar - this will list the contents of Supportability.jar
jar -xvf /opt/CA/APM/10.5.2.24/config/modules/jun/Supportability.jar - this will extract all the contents of Supportability.jar
jar -xvf /opt/CA/APM/10.5.2.24/config/modules/jun/Supportability.jar ManagementModule.xml - this will extract only the file ManagementModule.xml from Supportability.jar (which is what you need by the sound of it).
NOTE: Every xml file inside a MM jar file will have the same name of ManagementModule.xml i.e. the xml file does not share the same name as the MM jar file
Hope that helps
Regards,
Lynn