Currently there's only 1 function “hook” in the pbsurvey extension. This hook is called when the question item “Call user defined hook” is inserted in the survey. This can be anywhere within the survey.
Read the article how to use and implement your own classes and functions to use with a hook. You can find it at http://typo3.org/development/articles/how-to-use-existing-hooks/
Hook for processing the extra item is availble in the function callHook() and has the identifier “processHookItem”
If you have any suggestions for new hooks, please let me know.