What type of power does Jody come to represent in the scheme of the book? In what way does Hurston relate power to language?
Your question rather expertly identifies one of the key themes of the novel and the way in which Jody, in his relationship with Janie, exemplifies that theme.
Jody can be considered to be the opposite of Tea Cake - he is cruel, not interested in Janie and conceited. Jody finds his own identity in his holding of power over other people - that is to say, he is only happy when he is able dominate other characters and is over them. Central to his own sense of self is the need to be a "big voice" and a force of "irresistible maleness". As Janie says, he is someone who needs to have his way all the time, to "trample and mash down and then die" rather than anything else.
Jody's life then is centred around means of domination: purchasing, bullying, building and politics. He marries Jody not for love but because of her use to him in his ambitions - she will be a suitable wife for a mayor. However, his notions of power require Janie to be a mere object, static and, significantly, mute, which prevents her character from developing. Interestingly, when Janie rebels against Jody's power and topples his secure sense of power, she also destroys his will to live, questioning the merits of basing our identity too much in our ability to dominate and our own power.
Thinking about language in the novel, it is clear that finding a voice is linked to finding your own identity. It is crucial that Jody suppresses speech, but Tea Cake encourages it - it is through their dialogue together that we see that Tea Cake loves Janie for herself - her own individuality, and that their dialogue expresses that they are on equal terms with each other. You will want to trace this theme of speech and also silence throughout the novel to see how it feeds in to the journey of Janie and her final self-discovery.