Poor you! This is a difficult play to get to grips with at the best of times and it seems that you haven't been given much help. I am going to give you an idea then for you to think about and hopefully you will be able to re-visit the play and explore this theme to enable you to have a topic to write about in your assignment.
It is very easy to focus on the negative, bleak world which Estragon and Vladimir inhabit, where life is reduced to just wasting time and waiting for death. However, I like to think of myself as something as an optimist and so for me an important theme you could explore is that of friendship and how it gives life and purpose to the otherwise bleak existence of Estragon and Vladimir. Interestingly, this play presents us with two individuals, who, reading between the lines, show that they need each other to survive in this alien environment. Exploring this theme would provide an interesting counterpoint to the perhaps more "obvious" themes of nihilism and death which seem to dominate studies of this thought provoking work.
I hope this helps. If I were you I would go back over the play now and examine the relationship between these two characters, particularly paying attention to their dialogue to consider how they support each other.