How should I approach a long piece of writing to be able to answer questions about it?

The best way to approach this is to skim-read the piece first, highlighting/making a note of what you think are the most important concepts or issues raised. Don't stress if you don't understand some of the words: try to read senteces as a whole as this will help you make sense of what you are reading and it will also give you more context so that you are better able to "guess" what those words mean. You should then read through the questions to get an idea of what you're looking for exactly in the text and compare that with what you highlighted previously. Finally you should read the text more carefully, keeping in mind what the questions are about and pick out specifc parts which will help you answer the questions.