I'm not sure from where you are needing to access the path (ArcMap, ArcCatalog, etc) but here are a couple of examples:
'ArcMap
Dim pMxDoc As IMxDocument
Dim pFL As IFeatureLayer
Dim pDS As IDataset
Dim pWS As IWorkspace
Set pMxDoc = ThisDocument
Set pFL = pMxDoc.SelectedLayer
Set pDS = pFL.FeatureClass
Set pWS = pDS.Workspace
MsgBox pWS.PathName & "\" & pDS.Name
'ArcCatalog
Dim pGxApp As IGxApplication
Dim pGxObj As IGxObject
Dim pGxArray As IGxObjectArray
Set pGxApp = Application
Set pGxObj = pGxApp.SelectedObject
Set pGxArray = New GxObjectArray
pGxArray.Insert -1, pGxObj
MsgBox pGxArray.Item(0).FullName