Ok, go to the map, advance time to the evening.
- Click on the school. Who is outside the school that you can click?
- Click on all of them. Did that complete the task?
- If not, go inside the hallway. Who is inside the school that you can click?
- Click on all of them. Did that complete the task?
- If not, go inside the classroom. Is it still empty?
If it is still empty - there might be something else in another quest line you will need to complete to trigger that appearance to complete that task. If that is the case:
- Go in the library during "normal hours" and follow APoc1's usually correct advice: look for a strange book on one of the clickable book shelves. If that doesn't work - do the following:
- Go to bed.
- When you wake up, click on everything in every room in your home.
- Click on every door of every house you have access to.
- Click on every location on the map (motel, estate, bridge, homes, apt building, warehouse, Fox Club, bar, hospital, park, mall, diner, store, school, etc).
- Click on every door in the school, the store, the diner, the mall.
- Click on every tree, window, door, etc in Priscilla's backyard.
- Click on every NPC standing, sitting, whatever in every scene at every time frame of the day.
- And then go to bed, again.
- Repeat.
Be systematic, you'll find something to move forward.
They've already said no one was there in the evening.