How can we find out which products in the market are using a particular patent?

I'm not exactly sure if you have a clear understanding of what patents protect - patents do not necessarily protect particular products per se, patents protect particular structures or methods. So, for example, if INTEL has a patent on a particular microchip, that microchip can be used in desktop computers, laptop computers, iPads, iPhones, whatever. The patent protects the chip per se, that is, its structure, not the product within which the chip is embedded. It would seem to me that you would be more concerned about whether or not a particular patent exists for your particular product/structure than what products are using a particularly patented device, product, or structure. In the same vein, you must become aware of any patent that you may infringe, meaning that your product or structure comprises the same product or structure covered/protected by that patent.

If your concern is freedom to operate, you are not concerned with "a patent" but with all patents which might be infringed by your product. A freedom-to-operate search and analysis would be appropriate. If you are concerned about IP associated with a particular competing product, and seek to find out what relevant patents are held by the competitor, you need to find relevant patents held by or assigned to the competitor and relevant patents licensed to the competitor. Often this entails searching advertisements, magazine articles and other statements by the competitor in addition to patent searching. Sometimes there is a press release that mentions a specific relevant patent. Access to a set of databases covering newspapers, magazines, industry publications, press releases, etc., retrospectively, is very useful. Also, many patented products have a notice printed on the packaging or the article stating the relevant patent numbers or application numbers. Often I have searched PR Newswire, Business Dateline, Chemical Business NewsBase, and other sources. As far as drugs are concerned, the FDA (online) Orange Book is also a useful resource.