How do you ground a dishwasher with only 2 wires available?

If it has a metal body you attach a suitable cable to match the ground or earth wire colour in your country ( such as a 6 mm squared cross sectional area ) copper cable with green-yellow ( in the U.K.) insulation colours to the metallic frame of the dishwasher with a cable lug and a brass ( preferably ) nut & bolt. Then using a suitable length of cable to the nearest grounded piece of metalwork such as a copper pipe using a "earth clip" for a copper pipe. These can be bought from electrical wholesalers who supply all electricians or / and electrical contractors.