There are two kinds of titles, the window title and the title shown in File → Properties. The code below gets both.
Dim oSM, oDesk, oDoc As Object
Dim oFrame, oDocProps As Object
oSM = CreateObject("com.sun.star.ServiceManager")
oDesk = oSM.createInstance("com.sun.star.frame.Desktop")
oDoc = oDesk.loadComponentFromURL("file:///path/to/document.odt", "_blank", 0, arg)
oFrame = oDoc.getCurrentController().getFrame()
Console.WriteLine(oFrame.Title)
oDocProps = oDoc.getDocumentProperties()
Console.WriteLine(oDocProps.Title)
The document title is one of the attributes of XDocumentProperties.