questioner; interrogator
A person who asks a question, especially in a formal setting like a meeting, interview, or survey.
After the lecture, several questioners raised their hands.
All the questioners in the survey were students.
質問者 simply means 'the person who asks a question', while 聞き手 in an interview context implies an ongoing role of drawing out answers.
Compound of 質問 (question) + 者 (person).