Hi. You did not submit the text to which this question refers, which makes it impossible for it to be answered. However, I will try and help as best I can.
Generally speaking, we can state that the words that demonstrate the formal choice of words used by Douglass are the elaborate, cultured words that are only used in very formal and respectable environments.
Since you didn't enter the text, it's not possible for me to show you these words, but you can find them by reading the text and selecting fancy words that are not often used in an informal and relaxed environment.