When do you have an Exodia in poker?

If by Exodia you mean a group of cards that can signify an automatic win (based on the Yu-Gi-Oh! card game), then there is no equivalent in a normal game of Poker. If all cards are played at face value, then there is no cards which will ensure you a winning hand. There are certain groupings of cards which will highly increase your chances of winning (a royal flush is your best bet), but there is no automatic win in a normal game of poker.