I don't quite remember, try talk to the shop owner, the village leader, the kids. so basically every NPC in the town. This was what I did when I stuck.
If you already have the adult book you can read it during nighttime, when the brother is asleep.
If you need the book you can buy it from the people in the inn, bottom middle room.
You raise your potential for exposure by spamming the repeatable groping scenes from the rest of the village.
You need to read adult book 1 to raise level to 1, adult book 2 to reach level 2.
The Exposure Potential is the one stat you can't check.