Originally Posted by
Genius1
NZ depart from T1, and SQ depart from T3. You can only enter the airside area (where the lounges are) of the terminal from which you are departing (ie. T1 in your instance).
In T1, there is one shared Star Alliance lounge, which has separate Business Class and First Class lounges within it. Flying NZ J will permit you access to the Business Class lounge.
Actually, NZ puts its Business Premier passengers in the F side of the *A lounge there in T1.