If you use the following loop you can get an idea of the object keys available to you.
In the objects value, try also; task, task.workflow
Shall give you something like

so by doing logInfo(instance.label); It gives me the workflow title (screenshot https://db.tt/c1JVowRuhd )
Try playing around with these objects, not sure how to get the campaign name, because i am testing it on a normal workflow.