The following code can be used in the run script activity of the workflow to update the work notes or any other fields of all the catalog tasks [Conditionally we can update the catalog tasks as well]

var catalogTaskGR = new GlideRecord(‘sc_task’);
catalogTaskGR.addQuery(‘request_item’, current.sys_id);
catalogTaskGR.query();
while(catalogTaskGR.next()) {
catalogTaskGR.work_notes = “The ServiceDesk team has started working on this”;
catalogTaskGR.update();
}