To view the sales or other events relating to a product, locate the product with the explorer tree, right click the product, select View > Product Audit.
By default every product event will be shown. You can filter the audit by clicking the filter symbol on the column you wish to filter by. To view sales, filter the action column to show Sales. You can now see all sales for the selected period. To change the period you can use the date selector above the audit.
It is worth noting that if you have a period set on the top explorer bar this may already filter the system down. If you do not see the results you expect, try changing the overall period to 'All Time'. You can refresh the audit with the refresh button on the toolbar.