Just look on the Government website or do google Search and you will find all the instructions. Basic point is the employer must advertise for at least 4 weeks and continue to advertise for local applicants until the LMIA is approved. Employer must prove he cannot find any local PR or Canadian citizen who meets the requirments, then it gets into lots of things about the employer and wages must be at or above median wage rate for that region and NOC. So if you are on a PGWP you would take a chance that you could lose your job once it was advertised for the purpose of getting LMIA.