The internet is a wonderful thing. A simple search allowed me to find where the Prometric testing center is in the Philippines, and would allow you to do the same.
There are two tests for DataStage certification, one for
version 7.5 and one for
version 8.0, which you would find by searching for something like "DataStage certification" on the
IBM web site - there is even a link from there to a list of Prometric sites world wide!