It's a bit late, but you may have hidden the layer editor on accident.
Primarily, you should hover your cursor over the bottom border of the channel box and see if it highlights the same color as in my screenshot. This is a fully collapsed panel. There's a similar hidden panel in the outliner. If it highlights, click and drag it upward to pull it back out. It will snap to its minimum height, then grow smoothly like normal. Otherwise make sure your prefs and UI element settings look like the image.