My guess would be since it is a lab essay and he got zero he must have completely misunderstood the lab experiment and/or not understood the rubric. If it would me since he seems to be completely at a loss where to start I would ask him for the assignment and the essay. After that you might be able to see something that would help you guide him in his next steps. I suspect there is a huge piece of missing information here that would help you understand the situation better.