Workflow reports can be generated in two ways. You can either hover over the "Contact" icon on the workflow chart (image 1) or navigate to the "Contacts" section under every workflow to find the reports. (image 2)
The Workflow chart gives a broader view of how the contacts entered the Workflow. From the Trigger to the conditions and the actions, you can find how the contacts passed each phase of the Workflow with this type of Reporting.
You need to click on the "Contact" icon at every step as in the below screenshot to see what contacts were added due to the Trigger to which contacts qualified the conditions.
Apart from this, you can also generate a simpler version of the Workflow by navigating to the "Contacts" section of the Workflow. Here, you will be able to see the list of contacts that entered the Workflow and the date when they entered the flow.