[align=center][color=!shortcuts][insert=menu_location:mesh.select_coincident_vertices]
[insert=menu_shortcut:mesh.select_quick_menu], Alt+V
[/color][align=left]
Selects all vertices in the document which share a position with another vertex. This is not always a topology issue, but can happen accidentally when scaling an object to a size of zero, using [link=operation_split_vertices]Split Vertices[/link], inserting multiple vertices at the same position, when applying mirror clipping, or other similar situations.