You access an ISearchSchema interface object by calling the IBuildCatalog.Schema property, as in the following example, where objSearchSchema is the name you give to the ISearchSchema interface object:
Option Explicit
On Error Resume Next
Dim objSearchAdmin, objBuildCatalog, objSearchSchema
Set objSearchAdmin = CreateObject("Search.SearchAdmin.1")
For Each objBuildCatalog in objSearchAdmin.BuildServer.BuildCatalogs
Wscript.Echo objBuildCatalog.Name & "'s schema has " _
& objBuildCatalog.Schema.Columns.Count & " columns and " _
& objBuildCatalog.Schema.StopLists.Count & " stop lists."
Next
'Release objects
Set objBuildCatalog = Nothing
Set objSearchAdmin = Nothing