(Cura setting) How can I fix this? No top layer
I'm pretty sure the yellow lines are showing the full path of the extruder head, including where it's retracted.  Somewhere in Cura's maze of menus, there's an option to turn on/off various displays related to the slicing.  

As to why the top layer isn't there -- most likely it's too thin in your source  model.  You might try enabling "Print thin walls" options in the Preferences advanced list.  BTW, if you post the original STL or CAD file, we might be able to provide more accurate diagnosis.