When campaigns reach spam or junk folders, they are classified as being delivered. This means we do not receive a bounceback message, and therefore we are not able to specifically report on whether the messages went to the inbox or to another folder.
One place you can monitor for delivery issues is the Domains report (under Delivery tab). You can track this report over time to identify those domains where there could be delivery issues. If you notice that over several campaigns there are domains with zero views, you may want to reach out to those contacts to request that they add you to the safe senders or white list and/or you may want to change that domain to plain text delivery format to see if that increases views.