If you click on the Formatting tab from the top center of your screen in Atticus, you’ll see a previewer in the right panel. If you select Print from the dropdown menu above the preview you can select the Print option to see an exact representation of how your book will export in Print.
Once the print preview fully renders, You’ll find the total page count of your book displayed beneath the preview. This includes all your front matter pages as well, so it will be different from the page numbers on your book.