What's the content of the book that Aya read at the end of Mad Father? In the last scene of Mad Father game, Aya looks like reading a book that was lying on the ground, but she didn't explain to us what she read.

What is the book that Aya read at the end of the game?
It's implied that the book she found was one of her father's. One end of the game has Aya opening a practice up with Maria afterwards. 

She tells a patient that "She has lovely eyes", and given her father's tendency with body parts, I think she continued his experiments.

Because of this, I say the book is one containing her father's research.