HI Prabhakar
When I was with JDE/PSFT/ORCL consulting, we were asked this question on every new project. My response was always the same - if JDE touches it, it's going to be part of the CNC admin's responsibility. This means the DB, the network, the web servers, the printers, the app servers, the desktops, the browsers, etc. The CNC Admin role typically becomes the center of the JDE universe because he/she is responsible for keeping the system up and running. Does this mean you need to know all there is to know about these areas? Not at all. But you will need to know how to diagnose any issue that comes up and determine which of the other support groups should get involved (DBA, sysadmin, etc).
In a large company, the CNC admin is like a triage doctor in an emergency room: identify the issue, determine who needs to fix it, and then hadn it over or work with that person/team to resolve it. In a smaller company, the CNC person not only has to diagnose the issue but then is usually the one who has to resolve it. It can be overwhelming at first.
If you haven't done it already, I strongly suggest looking into the formal CNC courses offered by Oracle. These classes can give you the concepts, theory, and general how-to for most issues. However, experience is the best teacher once you understand how the system works.
Good luck!