There is access control to notes : acces is inherited from Item (Ticket, Activity,...) rights, adding a note being considered as an update to the item :
- if user can modify the Item, he can add a note to it, else he can't
- A user can only modify his own notes, and see notes from others, but can't modify others' notes
- V2.6 intoduce notion of privacy : user can add a note that others can't see, or share it only with his team.

So, what will happened if one user (user1) added note. Item then assigned to another user (user2). Can user 2 delete or modify note created by user1?

So, what will happened if one user (user1) added note. Item then assigned to another user (user2). Can user 2 delete or modify note created by user1?

No, a note is some kind of comment done by a user. No one can change what he said. Only user1 can change his notes, but can still do it even if he's not responsible for this item.

Thank you very much - very useful!
Regards,
Evgueni