Since William Golding's novel is an allegory, the main characters represent types and objects are often symbolic. So, as another suggestion for the double entry journal, you may wish to look in Chapter One and then some later chapters for descriptions of such prominent characters as Ralph, Piggy, Jack, and even Roger, who is by nature sadistic.
In Chapter Four, for instance, there is a short passage, perhaps of interest to you, in which Roger wants to throw a stone, "that preposterous element of time," at the unsuspecting Henry, who plays by the seashore. But, something prevents him from hitting Henry because his arm has been "conditioned by a society in ruins that knew nothing of him."
You may wish to look at the themes and the style of Goldings novel by clicking on the sites below. With these themes in mind, you, then, can find some relevant passages.
So a double entry journal is essentially two columns on your piece of paper. Draw a line down the middle to note this. On the left side, write your quotes that you choose to analyze. On the right side, write what you think about that quote. It sounds as if your teacher is specifically asking you to analyze diction, which the author's word choice.
An example of a quote is this: "The creature was a party of boys, marching..." This is what I would write on the left. This is a quote from chapter one.
Now, at enotes, we can't do your work for you. But I have picked out a quote that is short and that you should be able to identify a few words that are used either figuratively or differently than they usually are. Most specifically, I am referring to creature and party. Write what you think he's doing with these words in your response side.