How can I write an essay comparing and contrasting how the the theme of assimilation is used in two literary genres?
This assignment sounds like a "theory/application" essay. In other words, you are required to apply some flavor of post-colonial theory to two literary works in order to see how those works address the theme of cultural assimilation of the colonized subaltern into dominant discourses.
Your first step is to select the cultural theory model you intend to apply. You might choose work of Spivak or Said, for example, as a theoretical perspective.
Next, you need to select two literary works of different genres. The assignment will be more manageable if you choose two from the same culture, e.g. a novel and a poem from the Caribbean or a play and a short story from Indian dalit literature.
Next, show how the generic demands of the literary works yield different techniques of portraying assimilation.