Choose Surfacing tab→Surface group→Stitch list→Show Non-Stitched Edges button 
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Select a construction surface. The edges which are not stitched to an adjacent surface highlight.
Tip:
The Show Non-Stitched Edges command is useful when working with imported data. For example, when you import a set of surfaces that appear to form a solid body, but do not stitch properly in Solid Edge, you can use the Show Non-Stitched Edges command to determine where the non-stitched edges are so you can repair them.