What is the correct pronoun for this sentence: "__________ will attend the meeting is uncertain?"

The correct pronoun in the sentence "__________ will attend the meeting is uncertain" is "Who" because it is used to refer to people and is appropriate in contexts where the subject is uncertain. This sentence conveys that there is ambiguity regarding the identity of the person or people attending the meeting.

Using "Who" fits naturally as it interrogatively seeks to clarify which individual(s) will be attending. In contrast, "What" typically refers to objects or concepts, "Which" usually applies to choices or specified items among a group, and "Whose" indicates possession rather than a subject or agent. Thus, "Who" is the most suitable choice for constructing a grammatically correct and contextually relevant question about attendees.