I like this question! I have also wondered about POV for notes, and this is what I’ve settled on for now:
If I’m writing to understand some set of facts or ideas, I’ll use third person because I am an academic, and that writing may end up in a paper later on. Even if it doesn’t, I prefer the practice of writing more formally when it comes to science because that is ultimately how I will have to communicate most ideas I have or understand. Given that good, active third-person is hard to write, I like to get as much practice as possible.
I will sometimes use “we”, but only when I am writing about cross-cultural human behavior. I’m a social scientist, so I write about human behavior all the time, but it feels weird to refer to humans as “they” since I am, as far as I know, also human.
If, however, I am writing about productivity or personal philosophy or something that is directly applicable to my life, I have the tendency to write in second person but actually try to write in first person. For instance, on first pass, I might write something like, “You should explain the purpose of each source that you read.” However, the psychology of writing it and even re-reading it later makes it feel like it is advice to someone else because it always feels like I’M the one saying it, which means I’m “talking” to someone else. It never feels like past me talking to present me.
So, I will re-write such as statement as, “(I should) Explain the purpose of each source I read.” Now it sounds like me thinking about what I should do, not what someone else should do. It feels more personal, more like it is about me. I don’t always put in the effort to re-write “you” statements as “I” statements; sometimes I am fine with “you” statements for general advice that I haven’t decided to personally adopt. But once I want to put it into action, I suspect “I” statements have more sticking power.
Just my 2 cents…