Is there a method via the API to retrieve the URL of an in-course activity by its common module id?
Not that I am aware of. You could of course generate it in code by getting the course module object determining the module and calling the module's view.php script.
Well, the URL will be
Where cmid is the id you have. So, you just need the type of activity (e.g. forum/quiz). There must be a web service that includes that in the return.
If you have any specifics on how to dos this I would appreciate it. Either by web service or directly.