What is the nln exam?

The NCLEX-RN exam (National Council Licensure Examination for Registered Nurses) is a standardized exam that nursing students in the United States (and internationally, for those seeking US licensure) must pass to become a Registered Nurse (RN). There is no exam called "nln exam". There's a possibility you're thinking of a different acronym, or perhaps misspelling it. The NLN (National League for Nursing) is an organization that supports nursing education, but they don't administer a licensing exam.