Place a lightweight metal object on a wooden table. Suitable objects are metal shavings, paperclips or needles. You want the object to be light, so even a weak magnetic force can visibly influence the object.
Move the objects close to each other and watch if they attract one another. More than likely, they won't, but this test eliminates the possibility of reactions due to the object's magnetism, rather than the iron's.
Hold the iron just over the metal object. Try to keep it from directly contacting the object, because you may not be able to tell if movement is due to magnetism or physical contact.
Watch how the object interacts. If it moves or jumps up to the iron, then the iron is magnetized.