The ones with ** next to them are hints for the future locations of spells to be released - or places i put one already but forgot i did :/
1+2 relate to areas near spawn.
Tho I just realised there is two public mines, the second one gives you access to the same area as hints 5 and 9. And is near a forgotten surface city.
The numbered ones all should be a hint to current spells tho. Such as the walkway spell or the blink spell.
If you are lazy hint 8 is a sorta catch all hint, plays who have found (or been given special) spells - including the teach spell can take you on as an apprentice and teach you the spells they know. Generally tho gameplay wise it is expected they charge you money to teach you spells that may have taken them ages to find.
The repair spell is also the only spell people at merchant rank can learn and cast. (sorta used like a trade skill)