Hmm, if you don't mind me asking, why didn't you just ask your teacher that question? That's what teachers are for, right?
If the question really just says "discuss the brushstrokes", that's exactly what you need to do. I don't want to do your homework for you, really, but a good point to start would be to state that you can actually
see individual brushstrokes and then go on to questions like "How do you imagine Munch painting it? Does it look like he spent years working on the details, painting with a very fine brush?" Also, the picture probably had some sort of effect on you when you first saw it. Do you think that effect would be the same if you couldn't see the brushstrokes? Describe what the brushstrokes look like and what they do. Are they straight and and neat and is the entire picture covered with paint? You know, that sort of thing.
Another thing you might do if you don't mind a bit of extra work is to look at Munch's other
Scream pictures (he painted and drew the same motive several times) and examine how the strokes differ from version to version. Or do they not differ at all, perhaps?