About the ACM and IEEE-CS Computing Curricula I've been searching for a detailed definition about what computer science is about for years, when one day I came across these
two documents: Computing curricula 2005 report and Computer Science Curricula 2013.
The latter, more importantly, lists the knowledge areas and their relative content that an undergraduate student in computer science should know.
The content of each knowledge area is divided in core-topics and elective-topics.

What I want to ask is:

1) What exactly are the knowledge areas? Are they the fields of computer science where Ph.D. students can focus their research?
If yes, then how about architecture and organization (AR)? Isn't it the knowledge area where only computer/electrical engineers can focus their research?

2) Is this curricula applicable worldwide or does each country have its own?

3) Some topics are elective. How can I study the elective topics I'm interested in since my university didn't have enough time and resources to teach them?

Any answer will be appreciated.
The professional societies publish Curriculum Guidelines simply to guide universities in setting undergraduate curricula. They may be used by anyone, anywhere, but are not, normally, required. Note that the societies are private membership organizations, not official bodies. You can join them if you wish, but there are membership fees, normally less for students. 

The guidelines are created periodically (say every decade) by volunteer committees and try to represent a consensus of professionals. Each version goes through several published preliminary versions that anyone can comment on. The comments are considered by the committee. 

The goal of the committee is to design a "model curriculum" that is appropriate for either advancement to graduate school or to industry employment if a student has, at least, most of the knowledge implied. 

It is not, in general, a guide to PhD study, but those starting a doctorate should already have solid background in all of the areas of a model curriculum. 

Some university CS programs are accredited by ABET, which has its own expectations for curriculum as well as faculty standards, etc. This is a bit more official, but still not required. ABET is another private organization. 

If your university doesn't have courses in some area, you can ask them what can be done to "fix" that. You can also seek instruction in the missing areas through private instruction, another university, or online courses.