There are two ways to duplicate existing assessments already attached to a session/series.
Through the series page:
Go to the series that you'd like to duplicate the assessment from and go to the "Assessments" tab on the left-hand side.
Click on the blue "Review" button next to the assessment's title.
Click on the three dots next to the assessment title (on the left-hand side) and you should see a "Duplicate" button. Click on it.
Through the Tutor Tab
Go to the Assessments tab (https://schoolhouse.world/tutor/assessments)
Click on the three dots next to the assessment title (on the right-hand side) and you should see a "Duplicate" button. Click on it.