Follow the strategy I drew on this map: in order starting with brown, follow the brown lines first ( to find watermelon just in case), then the red lines (go type in the first elevator code into the elevator), then follow green lines, then the indigo lines afterwards (try to keep up with the indigo lines since they're so long, don't get them mixed up with each other and try to avoid following the indigo lines in the wrong order. Try to get a flash bang too in case Marzia cock-blocks you before reaching the 10th notebook. As for the missing 8th notebook, maybe there could be one in the satanic pentagram room, the Doggos room, red key room (also blue key required to open it), or one in Viktor's room that none of us knew about, or maybe even more likely you overlooked a room (one of the two pink classrooms or the perpendicular-doored green classroom near the bottom of the map; I forgot which of the 3 listed classrooms was it in; has its notebooks on the floor on one side of the room, rather than on a desk, easy to miss.
