I think that different teachers/ instructors have different terms for tasks, so ensuring that that is clarity of expectation would be critical.  This might involve asking your teacher/ instructor what them mean by a reader response criticism.  I would suggest that the standard reader response is a small writing sample that reflects how individuals feel about a particular topic in a reading.  Perhaps, the response would focus on how a particular style was used in a section of the writing, or how a certain theme was developed.  It is not a formal writing piece, but rather driven by the reader's response or reaction to a specific section of writing or an aspect of a reading.  They are subjective and can be used to generate discussion with others or to begin the process of writing larger and more comprehensive and formal samples of work.