In the Drawing View,
1. choose View, Show Hidden Objects (toggle on/off). You will now see the line outlined in a light gray.
2. right click the hidden line (which you can now see) and choose Show.
3. repeat step 1. to hide hidden objects again.
If every you don’t see a drawing object that should be there
1. check to see if it is hidden with the steps above.
2. Choose View, Format View, Preferences tab and look at the Background Color. Sometimes, especially when working with CAD files, the objects might be drawn in the background color.
3. You can also look for the object in the Drawing Data Manager and expanding the Layer it is on.