As ridiculous as it sounds, there is no way to add text to these notes.
It would be handy though wouldn't it? To have a little note window that stays on top of other windows and lets you take notes while you work or do research. It comes with Macs but Microsoft added this as a tease I guess lol. They give you a note window that can stay on top of other windows but do not let you type into it.
Microsoft does not really put any time or resources into improving the user experience on Windows. It can be very frustrating. If you are stuck with Windows because of work, you have to use Google to try to find software to install that makes Windows a useful OS for work or play.
It is pretty silly that with as much money as Microsoft has and as many software engineers as they have they still can't do something as simple as adding a way to take notes and reference them while you work. You have to go buy extra software, make sure it is safe, keep it updated, keep the license for it updated, etc.. Maybe with another decade of development on Windows we will get the simple things like the ability to take notes ;)