What key words should I use in an "assess" question?
The answer to your question would really depend upon what exactly you are going to assess. Generally, when you assess something you are considering its value or worth. You may be considering how something relates to something else. In terms of the study of literature you may be asked to assess the author's use of particular literary device and how it relates to the meaning of the work, for example. In this type of question, you should state examples of the device and assess what the device does to enhance the experience of the work. In this case, assess means to explain. I don't know that there is a list of words that you should use when you explain something. The most important thing to remember when you are analyzing something to is continually ask yourself why you think something you have said is true, and then writing the answer to that 'mental' question.
The first suggested defintion above was about considering the worth of something -- think assessment. In this case, you might be determining if a piece of literature is good, or even better, what makes it good. Again, the key to successfully writing this response is about developing a higher order of reasoning for the points you are making. You may state that a story is good because ______________. That makes it good because _____, and that is important because _______. It may look like a lot of becauses, and they don't necessarily have to be actually in the statements, but good arguments extend the analysis to prove the validity of the statements made.
No matter what you are assessing, focus on proving your point, not on what types of words you think need to be in your response. I hope this helps.