Where can I find the IEEE list of research topics?
The IEEE makes their 'Taxonomy' available on line (linked to in their Author FAQ under the Publications page), but this is only a hierarchical list without the designations you have given to identify something as the C.2.1.h topic. Surprisingly (to me), neither the author kit nor the editorial manual discuss this hierarchy.

In contrast, for the American Institute of Physics, the PACS codes are available on-line at PACS 2010.