The Seen This Before talent in Book of Judgment page 55 says, "... The Adept may make an Intelligence test in place of and skill test with the Investigation skill descriptor". Does he need to have the skill and could substitute int or does he not even need to have the skill? If the later Scholastic Lore has the Investigation key word. Seems pretty powerful.

Yes I fully agree that it is powerfull. Of course, it is just at int level so no +10 etc. However you could rule that in your game the talent allows you to roll at half your int skill instead. Which seems more reasonable to me.