There are many forms of enlightenment. Some are scholarly, outer understandings, some are alchemical or longevity focused. The form depends on the linage.
In our lineage, enlightenment means to attain the original clear light state. When this occurs, the body is refined into pure radiant light and then reformed back into the physical form. This can be seen by sensitive or awakened beings. To get to this state you must first be aware of there is a path, then become illuminated to the truth by your direct experience. Your own cultivation can naturally brings you to this form of enlightenment with a true lineage like the KUNLUN System.