Hi, sorry for the late reply. I've just successfully completed my test and got the certification yesterday.
I've asked the person who was in charge there, he said that this test is required for all engineers/architects working in Qatar within the private sector. It is mandatory to pass the exam and get the certificate for all the concerned persons.

If you fail the exam, you could retry it, but there will be a big hassle to do it since you'd have to write a letter addressed to the minister explaining what happened and asking them to give you a second chance.

I don't know about the compliance, but as per the regulations of the 19/2005 law, it should be done.