For example, if someone said, "Who here agrees that cookies are amazing?" on a Youtube channel section for a video that is centered around baking cookies. My brain keeps jumping to the word truism, but that's for statements and is more related to whether or not a statement is factual or not.
A given noun OED
What is given; the known facts, situation, etc.
The answers to his question were a given: most everyone answered the same.
A given is detail or fact that is known to be true. As in: "It's a given that I'll always love you, no matter how annoying you are."
Focusing on the asking side of your question:
I call this phenomenon Can I get an amen?. It's the act of seeking affirmation by picking the low hanging fruit of asking a question that you know will be answered positively.
How great is coffee in the morning?!?! Can I get an amen?!?!
The people who respond are often referred to as an amen corner.
Related but not exactly is preaching to the choir which is speaking as though to convert people despite knowing they already believe.
Politicians do this all the time. When they do it, it's called playing to one's base. Asking questions of this type to stoke up the audience knowing that they'll agree with the question.
If you can afford to use two words, I would call this a leading question, one for which you already have predicted the answer. I prefer this over "rhetorical question", a question that is commonly not expected to be answered.
lead·ing ques·tion /ˌlēdiNG ˈkwesCH(ə)n/ noun a question that prompts or encourages the desired answer. "after a few leading questions about his earlier life, he talked almost nonstop"
This is also known informally as milking (an audience); the term is however hypernymic. Lexico has:.
milk verb [with object] ...
2.2 Elicit a favourable reaction from (an audience) and prolong it.
he milked the crowd for every last drop of applause
A favourable reaction is expected or at least hoped for. 'Working' an audience is a synonym.
This is slightly broader than you're asking, but in the context of your example, the term Engagement bait fits. Engagement Bait refers to content in a post or video that is included for the sole function of boosting engagement(likes, comments, shares, reactions) on the post in order to reach a wider audience.
Common examples include:
- Asking viewers for their opinion on trivial matters that don't aren't likely to lead to any meaningful discussion. ("Comment your favorite kind of cookie!", "Would you do __ for $1,000,000?", "Would you try [product featured in video]?", "Pineapple on pizza. Yes or no?")
- Asking simple questions that one can easily infer or find the answer to. ("Do you guys like cookies?", "Why does my dog tilt his head back and forth like that? Comment below if you know ")
- Deliberately including typos, incorrect grammar, or parroting common misconceptions to bait commenters into "correcting" you.
- Encouraging viewers to "tag a friend who ____"
- Asking viewers to "vote" on a matter using likes, comments, or reactions.
- Misleading viewers into liking a post (common on instagram, where posts will try to trick you into double-tapping an image to "reveal" non-existent hidden content, or combine with the heart icon to create a "secret image")
- Challenging viewers to spell a word letter by letter in sequential comments.
Facebook seems to have popularized the term, so most online definitions are specific to that platform, but it is common on nearly all social medial platforms.
Considering this question was tagged as a single-word-request, I'm suggesting prevalent, particularly in the first meaning of Merriam-Webster's definition:
Groupthink: A psychological phenomenon that occurs within a group of people in which the desire for harmony or conformity in the group results in an irrational or dysfunctional decision-making outcome.