The concept of a "Dragon Knight" is not a specific Pokémon or character in the game.
* Dragon-type Pokémon: You can find various Dragon-type Pokémon in FireRed, like Dratini, Dragonair, and Dragonite.
* Knights: The game doesn't have any character classes or roles like "knights."
If you're looking for a specific type of Pokémon or character, you may be thinking of a different game or a fan-made concept.