In the Catalog, you can click on any sales channel on the left sidebar. You will see the following statuses appear:

In order to optimize your listings and get more SKUs listed to that channel, focus your attention on the "Not Listed, Listable", "Not Listable", and "Channel Errors" section. You can click on each SKU in each of these statuses and scroll down the left sidebar to see any "Critical Issues" and "Suggested Improvements" that are preventing you from listing your SKUs.

You can also go to the "Product listing errors" page and download the set of errors you would like to take a look at.