Sketcher > Sketcher Diagnostic Tools > To Detect Overlapping Geometry
  
To Detect Overlapping Geometry
Use the Highlight Overlapping Geometry diagnostic tool to detect and highlight geometry that overlaps other geometry of an active sketch or of an active sketch group. Overlapping entities appear in the color set for Highlight Edge.
 
* The tool does not highlight overlapping construction geometry nor does it remain active.
To show entities that overlap, click Sketch > Overlapping Geometry.