I was able to set Process variables (see attached picture), and set them in the process main:
params.put("Command", workflowName);
params.put("Parameters", null);
// start a new process instance
ksession.startProcess("process https://community.jboss.org/servlet/JiveServlet/downloadImage/2-778114-19919/450-450/pic1.png ", params);
System.out.println("Process started ...");
but variables are not availabe in taskHandler!