If you have launched Sketchbook Pro and can't find the layer editor, brush palette, a secondary toolbar, or open the Brush Library and the window doesn't appear, it is likely that the window has opened offscreen.
Resetting the layout back to default will bring missing windows back into alignment.
Go to the menu bar and choose:
Window> Default Layout
Once everything looks correct, exit Sketchbook Pro completely and restart.
Sketchbook saves your window locations on exit, so exiting and restarting should keep windows where you want them to appear going forward.