What are some of the major themes in the book "writing on my forehead" by Nafisa Haji?

I haven't read that book, so I don't know. But here is a good collection of literary terms and their definitions -- including Theme -- http://www.tnellen.com/cybereng/lit_terms Look up the term and learn what it means.

Another way to think of Theme is that it's a "secret message" the author wants his/her readers to understand. The author wants you to get it! ("it" being the underlying message of the story)