The NCC certification test is quite basic, and covers all possible aspects and population range which you might encounter while doing advice nursing. I would advice this test, but to be successful, you will need to have a little review in the adult protocol area -- areas of focus specific to that test include key elements of recognizing emergent symptoms of suicide/depression, understanding the pitfalls surrounding assessing an elderly person by phone (this is often similar to the pitfalls of assessing a child, since an elderly person faces some of the same physiological and psychosocial elements). An example would be recognizing that an elderly person it at high risk for committing suicide.
Try visiting the websites linking you to telephone triage and even looking up "telephone triage certification" or "NCC certification" under your own online search engine. There are professionals who have websites that focus on resources to help you learn about this test, an outline of its contents, and fees and certification update.
There is information through the organization on how to obtain a manual. This manual, if studied thoroughly, will provide success in passing this certification test. There are portions of the test which most of us who have taken it will say is very fair and helpful, and portions that are too basic and not a necessary "need to know" subject. However, as a professional, seeking to improve your own quality of care, express you specific interest in telephone advice, professional attitude and perhaps the way you are seen by your peers or managers, this is an ideal option.
A final word on why to take it ---over time, the more people who take this exam, the more likely they will decide it is worth delving into sub-specialty telephone advice certification -- such as Pediatrics. Isn't that what we all want? Special attention to our niche in nursing?
I hope this helps.