Joseph Joestar is Jotaro Kujo's grandfather and is characterized here as being quite an idiot. His lines consist of him saying "oh no" or "oh my God" and such. His voice should be deep and sort of gruff sounding, definitely showing signs of his age. A good place to look is his voice in the English dub of the Stardust Crusaders anime. And his, what would be, Engrish lines should be as over the top as humanly possible, perhaps with an accent.