When julia wang quoted former u. s. social security commissioner dorcas hardy in her speech on reforming the social security system, she was using what your textbook calls testimony?

In this case, she was using what your textbook calls EXPERT TESTIMONY

Expert testimony is a testimony that came from someone that has a credential in that specific field.
Example of expert testimony: social security commissioner giving testimony about social security system, astrophysicist giving testimony about planet's orbital condition, Bill Gates giving testimony about the condition of software market, etc.