What is the best way to see contacts that are still engaged in a specific Journey (have not left). There are no "contact update" related activities that would make it easy to define who left already.
You could use the said Contact Update activity as the last activity before exiting the journey and update the journey's Data Extension. So you would have to:
- Add an additional field to the journey data extension, for example, "Stage"
- Add the Contact Update activity at the end of the journey and set it to update the "Stage" column with a value "finished"
You could actually add a Contact Update activity at every stage of your journey, to mark each activity that the subscriber was engaged in, for example, "Email 1 sent", "Wait for 1 Day", etc.