Hello !
The Prometric Exam can be taken in your home country .There are no added benefits if you take it in Qatar.First get a job in Qatar,then take the exam.After which,(passing), your employer will ask you to email scanned copies of certain certificates for SCH Evaluation.This process is time consuming and often a bit frustrating too,because of the time taken.Once that is completed,you will be issued an Entry Visa(visiting),by the employer.On arrival ,you have to undergo the manditory Medical examination for Hepatitis B,C and also HIV,plus X Ray for T.B.Once that is cleared ,you will have to go for Fingerprinting and then attestation.And then finally,you are eligible for an SCH,Nursing License ,which i valid for one year.(Renewable)

I hope this helps.
Best of Luck!