in fact CAN, when used to express possibilities, embraces the idea of GENERAL truth, known fact or a strong possibility.
- Airplanes can fall.
- It can be very cold here in the Winter.
- This plant can be eaten, but I wouldn't do it if I were you.
- I'm not letting you walk home alone. I'm driving you. This city can be very dangerous at night. (I know this city very well - strong possibility)
COULD - is used to talk about weak possibilities - when you are just saying something, but you are not sure or have any information to back up what you're saying.
- Whose phone is this? It could be John's. (just a possibility - just an option) - you can also use MAY
Whose notebook is this? It could be Nelly’s notebook.”
In your sentence, do not repeat the word NOTEBOOK.
Whose notebook is this?
I don't know. It could be Nelly's.
Feel free to ask questions