Your ability to find information will depend largely on whether a company is publicly traded or privately held.. This video explains the difference:
One easy way to find out? Use Wikipedia. It usually will show the company's ownership status next to Type in the overview box.
A public company has shares of stock that represent an ownership interest and are traded openly on a stock exchange like NASDAQ or NYSE. The U.S. requires public companies to report their financial performance and governance structure to the Securities and Exchange Commission annually. That makes research on many public companies easy to find.
A private company is a company that is not traded on any stock exchange. Private companies as a general rule do not have to file any documents with the U.S. Securities and Exchange Commission. Consequently, finding information on private companies can be challenging.