SEDE has been a great tool to poke into SE data. I have seen some saved queries on it.

• Is there a definitive [official] list of queries used for badges on there? [apparently not]
• Is there a way to distinguish/quickly find queries used by SE itself and not user-contributed queries?

Since there is no definitive list, how many queries like this one Legendary are available from questions/answers on meta?

Re badge queries (subset of question) >
Keep in mind that some of the badges depend on information that is not available in the data dump (like sportsmanship, talkative and so on)