Source : Webster's Revised Unabridged Dictionary (1913)

Whereof \Where*of"\, adv.
   1. Of which; of whom; formerly, also, with which; -- used
      relatively.

            I do not find the certain numbers whereof their
            armies did consist.                   --Sir J.
                                                  Davies.

            Let it work like Borgias' wine, Whereof his sire,
            the pope, was poisoned.               --Marlowe.

            Edward's seven sons, whereof thyself art one.
                                                  --Shak.

   2. Of what; -- used interrogatively.

            Whereof was the house built?          --Johnson.

Source : WordNet®

whereof
     adv 1: of which; "punishment for a crime whereof he was convicted"
     2: of what; "he knows whereof he speaks"