'Request hi-score board' just requests the hi-scores - they arrive a moment later. When they arrive, the Facebook object's 'On hi-score' trigger runs once for each hi-score. In this trigger the HiscoreName, HiscoreRank and Score expressions in the Facebook object are set so you can get the current hi-score e.g. "#1 - Tom Gullen - 1337". A simple way to list scores is to append that to a string object in the 'On hi-score' event, so when it triggers for each hi-score you end up with a full list of scores.
Note that if the user is submitting a hi-score, it won't appear in the hi-score board until the 'On score submitted' trigger runs. So you might want something like "On score submitted: request hi-score board" to guarantee the score the user is submitting will appear in the hi-scores.