I have a sub-report in Report Footer B. First of all how to reference the sub-report and then How can I reference the database object within that subreport from vfp.

First, you need to open the subreport object from your main report object:

oSubRpt = oMainRpt.OpenSubreport("subreportname")

Then you should be able to access the database object associated with the subreport, in the same general way that you'd access the database object for the main report.

oDb = oSubRpt.Database()

Let me know if that helps...
Kevin