You need to go to the Reports > View Sales Reports dashboard and in the Sales Report View make the quantity appear.
You can do this by right clicking on the Gross Profit tab and then at Show Field List:
You then need to drag and drop the Quantity next to the Gross Profit
Like so:
Then, based on the Select Columns options you can pick and choose which items the report will include. For example you can end up with something like this:
You can then also filter by calendar period like so:
