I need to ask some questions on cloud computing. I think Server Fault may be perfect place for such questions, but are there any specific Stack Exchange sites where can I ask questions on cloud computing?
These are your likely options:
Server Fault - related to cloud computing platforms that you might manage or configure your self
Stack Overflow - related to programming against a cloud computing platform or an API etc
Web Apps - needing help with a cloud based app from a user's perspective, not a developer's
Pro Webmasters - running a cloud based app on a third party server
But really, without more context it is hard to tell
As has been mentioned, without more context as to what you're asking about, it's hard to tell. You might also have some luck, if your questions are about using Cloud Computing for HPC or other scientific computing, over at the shiny new Computational Science beta site: https://scicomp.stackexchange.com/
While not live, there is a site proposal in the "Definition" stage for Practical cloud computing. With additional test questions, and clarification about what type of cloud computing question you are asking, this site may fit your needs if it enters private/public beta.