To quickly duplicate a task, including all details, files and subtasks, you just need to:
1) Click on the task name on the "Work" or "Project" view;
2) On the Task edit panel, pick the button to duplicate;
3) Edit the details on the new task.
This way you can add the same task to several people, and those tasks will be tracked individually by each one of them.
See how to duplicate a Task in this quick demo: