LRN is the Learner Reference Number that can be found on your Report Card or School ID.
SAT is the Scholastic Aptitude Test which is an international examination. If you don't have SAT result, just put 0 or leave it blank to proceed with your application.
Note:
Undergraduate applicants with Scholastic Aptitude Test (SAT) score of at least 1,100 will be exempted from paying and taking the MPASS.