A sage can spend a fate point to get an auto success on any lore test. Does this include forbidden lore?

It's clearly written as "any Lore test", just don't forget that all Lore skills are specialist skills, so you can't use them at all if you're untrained.

OK are you sure his talent only applies to lore skills he has? I'm asking as the sage description seemed to imply he might know some little bit of data about things he wasn't fully trained in.

Here's a quote from t he sage description.

Sages tend to know a little bit about everything; even if they have not studied the subject expansively, there is always a good chance that they have come across it in one of their other research endeavours.

Saying he knows a little bit about everything made me think his special rule about fate allowing him. A success on any lore test applied to all lore skills.

You can't roll skill test if it's specialist skill and you don't have this skill , and you can't use FP for impossible roll. Look at Recommended Advances at p.73 - why Sage would buy Lore skills if he can use them without training?

Well, because he can only get the auto success with a fate point and he may only have 3 of them and he may want to save them to survive in combat.

Well, for me RAW is very clear, but you can use any interpretation on your table...