Finding the declaration of a variable in Emacs

You can have Semantic / CEDET show you the definition of the symbol under point after a short delay in the echo area via semantic-idle-local-symbol-highlight-mode, also enableable globally for all buffers, and automatically via adding global-semantic-idle-local-symbol-highlight-mode to semantic-default-submodes.

Doing this for non-local symbols requires CEDET to know how to locate things in your project, which usually happens more or less automatically, particularly if you use etags or GNU GLOBAL.