The main purpose of this sort of reading response paper is simply to see if you have read the book. Thus the request for your own thoughts means that the instructor isn't looking for some "correct" response, but just a sense that you are reading the work carefully and thinking about it rather than just skimming over a summary.
One way you can approach this sort of assignment is by relating it to your own major or interests. For example, imagine that you wanted to work in automotive sales or repair. You might focus on the forms of transportation used throughout Marco Polo's journey. Alternatively, a premedical student might write about the health habits or diseases described in the text. Alternatively, you could trace Marco's path on a modern map and look at what has happened along that route in the ensuing years. If you like cooking (or eating), you might think about how this new trade route affected cuisine (pasta, for example, was actually invented in China and brought back to Italy) or some of the descriptions of food in the story.
Basically, choose one aspect of the work that interests you, and take notes as you read, and then write about your impressions of how the work treats that subject.