When you duplicate a task, you have the option to include a link back to the parent task in the new task.
However, there is no link from the parent task going to the duplicate in the Activity Log.
It would be really useful to have this, as then it would indicate that certain actions had been taken. I just went ahead and performed some actions on a task (moving it to an FAQ project) before realising another team member had already essentially done the same thing by duplicating the task.
I do see this post asking for the same thing a few years ago, See a link to my duplicated task from their parent task history but it has been closed.