I am assuming that what you mean is that you need a "thesis statement" for an essay on the novel that reflects the theme of prejudice and the impact that it has on the characters and their world views. If that is the case, then you might consider something along the lines of:
In her novel To Kill a Mockingbird Harper Lee examines the implications of prejudice on society through the interactions of her characters.
Then, you could look at the most obvious prejudice first. In this case, this would be reflected in the fact that Tom Robinson, as a black man, is automatically viewed as guilty of raping Mayella. Even when all the evidence seems to point to the impossibility of that fact, he is still declared guilty. her word is taken over his because, although she is poor, she is white.
Next, there is the prejudice against the Ewells on account of their social status or lack thereof. Prejudice does not only come in terms of race and ethnicity. There is also a prejudice against the poor in Maycomb who are viewed with distaste by all except Atticus (and later Jem and Scout). Atticus believes that pride and worth are not tied to money or race but to personal qualities such as kindness.
Another form of prejudice is that which is shown against the mentally handicapped. Boo is treated as a monster, shut away from a society that fears him because he is "not normal" - he is seen as less than human.
All three of these examples are still evident in our society today. People still view each other differently, often negatively, on the basis of race, economic status, or mental handicap. Mental illness, in particular, is still stigmatized. The world views Harper Lee presents in the novel, sadly, have not changed all that much.