I think it wants your name as in the passport so that when (if) you go to book flights on line or check in on line their system can autofill the information for you.
If you put First Officer Joe Bloggs, it may screw their system up.
It must ask for occupation somewhere, so long since I filled it in(!) but frankly if you have not got minimum PPS level qualification, upgrades are few and far between on SQ. I heard somewhere that they have 40,000 PPS level members in Singapore, and keeping them happy takes a lot of effort.
Mind you, I once knew a guy in UK who upon qualifying as an Actuary, had his cheque book re-ordered with Fred Smith FIA as his name. And yes, they can be sad w@nkers...