Yeah, it's a real challenge to identify some of these miscellaneous icons. There are millions of them, and there is a chance that someone in this forum has the same app installed so they'll recognize that icon, but that's really a hit or miss matter. Icons for popular apps will be easier for others to recognize, but most apps not so much.
But icons are just visual identifiers linked to specific, respective apps, so if you look through your Settings >> Apps menu listing see if there's any app with the same or at least similar icon. Most notification icons, being much smaller, will have at least some close resemblance, and may be scaled down replicas or altered in some way to reflect a notice or changed condition of the app/service.