These ftl files are typically packaged in a jar file and it is copied to CLASSPATH. In this example, these ftl files are located in
jbpm-gwt-form-5.0.0.jar that you can find in gwt-console-server war file (gwt-console-server\WEB-INF\lib\jbpm-gwt-form-5.0.0.jar).
You can find a simple example with a few ftl files with parameters here:
http://community.jboss.org/people/bpmn2user/blog/2011/02/21/jbpm5-example-for-forms-with-variables