IPA: /ˈkwɛs.tʃən.ər/
KK: /ˈkwɛsʧənər/
A person who asks questions, often to gather information or clarify something.
The questioner raised an important point during the discussion.
Questioner → It is formed from "question" (from Latin *quaestio*, meaning inquiry or a seeking of information) and "-er" (meaning a person who). A questioner is a person who seeks information or asks questions.
Think of someone who is 'seeking information' ('quaestio') — the '-er' just means a person. A questioner is someone who asks questions.