My GM is running Storm King's Thunder and decided that my Hermit warlock's discovery is knowledge about a place call the Eye of the All-Father. What stuff should my Warlock would know about it without all too many spoilers about the story.
There's an easy answer to this question that was brought up in the comments, but I'll put it down here with some of the reasoning why.
Ask your DM
While there is a chunk of lore and this story that you could research on your own, you never know how much of the story the DM is sticking strictly too, if there are things about the Eye of the All Father they may be different for your game versus other games versus story as written.
You also want to ask because your DM is going to know the precise answer as to how much your character would know. You're a hermit warlock, did you get the information on this because you were a hermit or because you were a warlock, that's going to change what you know. Again, this is something that you and your DM can figure out, because, as you said in the question, you don't want spoilers, you want to know how much you know.
Finally, if you are trying to keep the meta-gaming down so that the other players at your table don't know about the Eye of the All Father, e-mail/text/call/message the DM so that you can do it out of game so you know but the other players don't. That's going to give you be better idea than we're able to give you without having meta-gaming going on at the table.