If your AEM Process step is running, but not able to have a custom logger to log through you created a custom logger with your custom process step class along with that add the below classes to generate workflow loggers into your custom logger file
Go to AEM Sling log http://localhost:4502/system/console/slinglog create a custom log
com.adobe.granite.workflow.core.WorkflowSessionImpl
com.adobe.granite.workflow.core.job