Clearly the character that you want to focus on, who seems to be the main vehicle for the author's exploration of assimilation, is Beneatha, and in particular her relations with the two men who represent opposite extremes of the assimilationist debate: Asagai and George. One of the most powerful symbols of assimilation is the play is Beneatha's hair, and how, after some encouragement from Asagai, Beneatha chooses to wear it naturally rather than straightening it so that it looks like any "normal" hairstyle. Asagai uses harsh lanaguage to describe what she does to her hair, saying that she "mutilates" it every week.
Of course, George is the opposite extreme as he represents a black man that has embraced the white world and the white way of doing things and has become successful as a result. As his response to Beneatha's hair shows, he is an assimilationist as he wants to fit in to white dominated society. Note how he talks about her African past:
Let's face it baby, your heritage is nothing but a bunch of raggedy-assed spirituals and some grass huts!
Thus we see the two different views of assimilation advanced by Asagai and George, with Asagai having much more of an impact on Beneatha who remains interested and curious about her African identity.