An easy way to generate essay topics on a text is to consider the themes of that text and then use that as the basis of an essay. You can pick a theme and explore how it is presented in the text and what is said about it. If we consider the themes of this story, we can see that there are a number of possibilities.
Firstly, alienation and loneliness are key themes through the way in which the text focuses on the impact of a father's abandonment of his family. Pearl Tull is a perfect example of a character who is isolated from those around her and even from herself as she struggles to face the reality of being abandoned and raising her children by herself. Combining this theme with an examination of Pearl's character would make for a great essay topic.
Secondly, you might wish to think about the way in which the Tull children respond to their troubled childhood and the abuse that they suffer. Does the text suggest that we can ever transcend such childhood traumas, or do they haunt us for life? This would make the excellent basis for an essay question.