You can access Sprint Reports by going to the More tab in the top right. If you use Iteration as terminology, your view will show "Iteration" instead of Sprint. In the help articles, we use "Sprint".
To access report
Click on Analytics
Go to the Delivery By Sprints tab
For completed Sprints, the report is automatically visible in the Scrum of Scrums view.
View Report
"View Report" button appears automatically based on the sprint dates.
For the currently ongoing sprint, the button is visible, and next to the Sprint name, you will see "Active" to highlight it's an ongoing sprint.
When you access the Sprint report for the first time, the report is generated automatically based on the information available in the Sprint at that point.
You may regenerate the report anytime, and all the previous versions are accessible.
Accessing Sprint Reports in Scrum of Scrums
In the Progress section, drop-down lists all the Sprint names that are completed, and their report is accessible by clicking on the sprint name.