If you are asking which Centre, then you dont know about SANS/GIAC or GPEN details.
GPEN is hosted by SANS and SANS will come to Singapore thrice in 2017. SANS Secure March, SANS Cyber Defense, SANS SOS October. That doesnt mean GPEN is available. SANS has multiple courses and brings a few of them to Singapore every year. Your other options is do online via SANS ondemand or Self Study. Just be reminded to be prepared to fork out about 9k for Course+ exam. (With the high USD)
FYI. GPEN doesnt teach anything on Nessus. Nessus is a Vulnerability Scanner. GPEN teaches on Penetration testing. Both are totally different things. Some examples Metasploit, Meterpreter, Scapy, John the Ripper, Hydra etc.
Also SANS dont teach on commercial tools. Only Free open source tools for obvious licensing reasons.