To view all Z-Report from different POS of different locations, you can access to the backend and go to each POS to see the report history.
Goto Magento Backend > POS > Manage POS
Click Details to view all information about the POS that you want to view Z-Report
Scroll down to Closed Session then Expand to see all the generated reports for all closed sessions
Click to the details of the report and click on the Z-Report button to view it in the popup form.