public Workset GetActiveWorkset(Document doc)
{
    // Get the workset table from the document
    WorksetTable worksetTable = doc.GetWorksetTable();
    // Get the Id of the active workset
    WorksetId activeId = worksetTable.GetActiveWorksetId();
    // Find the workset with that Id 
    Workset workset = worksetTable.GetWorkset(activeId);
    return workset;
}

Public Function GetActiveWorkset(doc As Document) As Workset
    ' Get the workset table from the document
    Dim worksetTable As WorksetTable = doc.GetWorksetTable()
    ' Get the Id of the active workset
    Dim activeId As WorksetId = worksetTable.GetActiveWorksetId()
    ' Find the workset with that Id 
    Dim workset As Workset = worksetTable.GetWorkset(activeId)
    Return workset
End Function