Please refer to the following Advisory Circulars for the requirements for nominated certifying staff:

a) Advisory Circular AC 145-2 Initial Qualification Requirements for Certifying Staff.
b) Advisory Circular AC 145-8 Authorisation of Line Maintenance Certifying Staff.
c) Advisory Circular AC 66-9 Acceptance of Foreign Aircraft Maintenance Licenses for SAR-145 Maintenance Facilities outside Singapore.

The Advisory Circulars can be obtained here.