For meshes, when you go to edit mode, the default is vertices, but you can switch to edges and faces. For grease pencil, it’s similar, but the default, I think, is strokes. So you want to switch to points. Next to where it says Edit Mode, the 3 little boxes that when you hover over them say Points, Strokes, and Segments. (just like in meshes., points hotkey is 1, strokes is 2, segments 3). Once you switch to points, you should be able to edit them.
