If you hover your cursor over the larger buttons on your "ribbon" (it's usually in the bottom right), you should see a vertica list of icons for the child windows in that parent window. Click the icon and the panel will go back on your screen.
Activity tracker and path window default to top-left, so one of those sounds like what you're looking for.
Activity tracker and paths are under the Hero parent (looks like a shield and sword), and quest list is under the Adventures parent (icon looks like a compass),
You can also go into the relevant parent menu by pressing its button, and drag the header of the child window you want onto your HUD from there.