The easiest way to see secondary categories for any listing in Google Maps is to download an extension called GMBspy.
https://chrome.google.com/webstore/detail/gmbspy/hijfnlgdhfpmnckieikhinolopcolofe?hl=en-US
Once installed, you can go to any profile in Google Maps, click the GMBspy extension button and it will list out the primary category as well as any secondary categories. If there is only one category showing, then the listing has no secondary categories. The category at the top of the list is always the primary category.