The NMS is Canada's master library of pre-written construction specification sections. Every procedure, product, and method an architect is likely to encounter on a Canadian project has a corresponding NMS section, organized by MasterFormat. Knowing the NMS means knowing how the specification system works, not what any one section says verbatim.
Examitect's ExAC study plan lists the NMS specifically as "National Master Specification (NMS) - RAIC Table of Contents" for Section 3 category 8.5. That framing tells you what the exam expects: a working knowledge of how the NMS is organized and what each Division covers, not word-for-word spec memorization.
The NMS also provides the vocabulary that shows up across Section 3 and Section 4 questions: MasterFormat Division numbers, the three-part section format, submittals, and substitutions. Familiarity with even a handful of NMS sections builds that vocabulary in context.