The statistics of a Story are visible in your account for 14 days after posting. So it is important to share a screenshot in the assignment as soon as possible.
You can find your Story statistics as follows:
Go to your profile
Click on the 'Statistics' button in the middle
Scroll down to 'Stories'
Click on the Story for which you want to see the statistics
Swipe up
The statistics appear on the screen
Then take a screenshot of this and share it as an attachment in the assignment. Did you make multiple Stories? Then take a separate screenshot for each Story.