"It is what he is talking about."
Translation:C'est ce dont il parle.
"Ce" can also stand alone, it's the masculine singular demonstrative adjective.
"Ce" means "this" or "that" and is used for masculine words (eg. "ce mur" means "this/that wall"). "Cette" is used for feminine words (eg. "cette voiture" means "this/that car"). "Ces" is the plural form (eg. "ces chats" means "these/those cats").
These should not be confused with "ça" (don't forget to use the cedilla-c: ç!), "ceci/cela" etc. For more information, see: http://french.about.com/od/grammar/a/adjectives_demonstrative.htm http://french.about.com/od/grammar/a/indefinite-demonstrative-pronoun.htm
Maybe I misunderstood something or Iv already forgot it: but i remember one of the users telling me ce is an adjective it cannot stand alone only with a noun (ce voiture), cela and ca are pronouns so they can stand alone. So according to that, this should ne C'est ca dont il parle, if I am not mistaken.
http://french.about.com/od/grammar/a/relativepronouns_4.htm For more information : )