ValeDeOro
(@valedeoro)
Automattic Happiness Engineer
Products without a category are now marked with a -, like this:

This means that you should be able to easily spot the products without any category added. Alternatively, you can export all your products via Tools >> Export, open the csv file and then order the file by category. This will allow you to quickly add those categories. Reimporting the updated product file will update de products on the site. To find out more about how the import/export works, have a look at this guide: https://docs.woocommerce.com/document/product-csv-importer-exporter
We haven’t heard back from you in a while, so I’m going to mark this as resolved. If you have any further questions, you can start a new thread.