Here's a newbie question: I'm writing event observers for course_created, user_enrolment_created, and related events. If I put echos in for debugging output, where does that output go where I can see it?
If the PHP script is being run by the web server process, i.e. for a web page, then any echoed output goes to the browser so it's probably in the HTML source of the page.
Or, even better. Make sure xdebug is running on your local server, link it up to your IDE of choice and then set a breakpoint in the event observer and step through it - the (small) amount of time it takes to get xdebug up and running will be almost instantly dwarfed by the huge amount of time you save not having to add (and later remove) echo statements and re-run your code multiple times to figure out what is happening.