I opened up a project and I wanted to edit one of my Grease Pencil objects-- but it's not showing any of its layers in the Grease Pencil Channels. I clicked on another GP object in the same project and it showed the layers no problem. I unlinked all of the objects parented to the GP object in question, opened it up in a new file, made sure it didn't have anything animated, wasn't in too many collections, made sure I'm in the right menu, in draw mode. I can STILL draw, but I won't be able to see it make the new keyframes, or edit the keyframes at all. I'm going insane, I can't figure out why I can't see the channels for this object.
You have the option to "Only show selected" enabled. It's the blue arrowhead in the set of icons on the right of the graph editor.
If you disable it, then every F-curve you've created by adding keyframes will show up in the graph editor.
If you select an object that you've added F-curves to, by creating keyframes for them, then all of the F-curves for that object will show up in the Graph Editor.