Look at your mark scheme. Are asking you for a close textual analysis?
My guess is that they are as they have told you to only focus on one scene and not the whole of the play but you must double check this. Examine your question, the key words would be 'extent', 'present' and 'tragic hero'. Draft up a plan then centre your research around this. Focus on say 3 themes and go into detail, if it's close textual you will have to examine language, stage direction, structure. Say for example one theme could be that Othello represents naivety and innocence to an extent. The themes you wish to talk about will register as you read over the entire play and read the last scene closely. Good luck!