This is actually a rather vague question. When we think of the word diction, what is actually refered to is nothing more complicated than the choice of words that the author uses in his work. Therefore, what do you precisely mean or what do you want to find out? Looking at the novel we can see that there is a range of diction, including dialect in the speech that some of the characters use, to beautiful and amazing description of the natural world through which Inman walks and in which Ada toils. Slang and idioms are apparent in the dialect of some of the characters, and this certainly helps to recreate a picture of contemporary America during the Civil War. However, I would suggest that you either pick a specific passage and comment upon the diction used in that passage or try and narrow down your question in some way.