Where to look depends on which HP line you own. LaserJet printers show a short numeric code on the control panel, usually a number followed by a decimal and a sub-code, such as 50.1 or 59.40. DeskJet, OfficeJet, and Photosmart printers are more likely to show a plain-English message on their small screen or in a pop-up on your computer, sometimes paired with a longer code that starts with "0x."
If you have a numeric code, type it into the search bar exactly as shown, including the number after the decimal point where there is one, since 50.1 and 50.9 point to different causes. If you only have a message like "Cartridge Problem" or "Printer or Ink System Failure," type that phrase instead. Selecting your printer model first keeps the match accurate, since HP reuses some codes across very different product lines.