So the drawing view is referencing an assembly and the named sketch can be found in some parts in this assembly.
You need to iterate the occurrences collection. In every occurrence you should try to find a PlanarSketch with the required name and then create the appropriate PlanarSketchProxy object. You need to pass this PlanarSketchProxy object into the DrawingView.SetVisibility method.
The following VBA sample code illustrates this approach.
Sub Test_SetVisibility_Sketches_Assembly()
'active drawing doc
Dim oDrawDoc As DrawingDocument
Set oDrawDoc = ThisApplication.ActiveDocument
'active sheet
Dim oSheet As Sheet
Set oSheet = oDrawDoc.ActiveSheet
'the 1st drawing view
Dim oView As DrawingView
Set oView = oSheet.DrawingViews.Item(1)
'reference to the assembly document
Dim oAsmDoc As AssemblyDocument
Set oAsmDoc = oView.ReferencedDocumentDescriptor.ReferencedDocument
Dim oAsmDef As AssemblyComponentDefinition
Set oAsmDef = oAsmDoc.ComponentDefinition
'reference to some component (here it is the 1st)
Dim oOcc As ComponentOccurrence
Set oOcc = oAsmDef.Occurrences.Item(1)
'reference to the part document
Dim oDoc As PartDocument
Set oDoc = oOcc.Definition.Document
'part definition
Dim oDef As PartComponentDefinition
Set oDef = oDoc.ComponentDefinition
'sketch in the part context
Dim oSketch As PlanarSketch
Set oSketch = oDef.Sketches.Item(2)
'sketch in the assembly context - proxy object
Dim oSketchProxy As PlanarSketchProxy
Set oSketchProxy = Nothing
Call oOcc.CreateGeometryProxy(oSketch, oSketchProxy)
'make PlanarSketchProxy visible
Call oView.SetVisibility(oSketchProxy, True)
Beep
End Sub
Additional information you may find here
http://adndevblog.typepad.com/manufacturing/2012/06/include-sketches-from-sub-assemblies-in-a-drawin...
Proxy objects
http://modthemachine.typepad.com/my_weblog/2009/04/positioning-assembly-occurrences.html
http://adndevblog.typepad.com/manufacturing/2013/07/occurrences-contexts-definitions-proxies.html
cheers
Vladimir Ananyev
Developer Technical Services
Autodesk Developer Network