If you are trying to manually type in notes from the keyboard onto a front panel while the vi is running then forget it. Can't be done.
You could put a string control on the graph or anywhere on the front panel and type into the control while the vi is running. If you wanted multiple notes, you would have to create other string controls. Of course you cannot easily resize or move these controls while the vi is running. There is a way to add, resize, move controls programatically but it is complex and would be beyond the scope of this forum. Practice using event structures and property nodes. With these you could perform what I think you want to do. Here is an example of having one string control on a graph.
While the vi is running, you can click inside the text box on the graph and type in notes.