I though the SQ pay-f-get-c applied to 2 class SQ flights not originating or terminating in N America??? I guess with the exceptions on the SIN-ICN-YVR/SFO and TPE routes...I don't know first hand as I have not used awards on those routes.

As far as the OP is concerned, you should have no issues getting on the EWR nonstop to SIN and back in C paying C miles (90k). You would have to return transpacific to use the 90k award.

As another poster said, to return via SIN-FRA-JFK, it would be considered RTW.

You can also go to SIN via Europe for that 105k in C...