ElementInstanceKey
ElementInstanceKey identifies a specific running BPMN element instance inside a process instance.
For example, a service task, user task, event, gateway, or sub-process each has its own element instance key while it is active.
You use this key when an API call targets the scope of a specific element instance, such as setting local variables or searching for incidents on that element.
If you are working with an activated job, you can usually read this value from job.elementInstanceKey.