How to engage in discussion after a presentation on an unfamiliar topic? Sometimes I am in a conference presentation or seminar which there are only a handful of audiences, and after the presentation the atmosphere simply urges the audiences to ask questions or the presenter will be embarrassed. I do want to contribute to a meaningful discussion, but the problem is that I am unfamiliar with the topic, and after listening to the presentation, I can only understand the background briefly. I cannot formulate a good question after the presentation.

You may wonder why I attend a presentation which the topic I am unfamiliar with, and sometimes it is driven by curiosity, and sometimes it is compulsory (like invited speakers from my supervisor etc). I know it may be possible to formulate a good question by reading the publication of the speaker beforehand, I have tried it actually but the efforts to understand an unfamiliar topic seems too much, and it may not worth it especially I cannot come up with a good question afterwards.

I don't want to be looking stupid after a presentation, but also don't want to start a discussion which is not quite meaningful just because nobody raises a question. Is there any way to help one to start a good discussion for a topic which I am unfamiliar with after a presentation?
In general I agree to what @user46345 and the others said: If you do not have a good question (and no good reason to ask one anyway) it is better to be quiet.

However, sometimes it is important to ask a question. Two examples that come to my mind are:


You are the discussant of the talk (and you had no opportunity to read the paper before the talk or the speaker already answered all your questions in his talk).
You have a very shy audience that whats to ask questions but no one wants to be the first one to ask.


But there are probably others.

The best thing to do would be to read the paper first and think about a question related to it. If that is not possible there are still some other options to use:


If you haven't understood something during the talk: ask about that.
It is not your field of expertise, so no one expects you to know
everything about it.
In most fields a very common type of question is about applications. In economics this could be "What are the policy implications
of your results?". @JeffE has the following examples for (theoretical) computer science "Does your algorithm work well in practice?" and for non-theoretical computer scientists "Does your technique have any theoretical guarantees?".
"Sensitivity analysis type questions": Is the assumption A crucial?
How would your result change if you change assumption B? They still
require some knowledge of the subject but not as much.


These questions can be used as backup as long as you still have some knowledge about the topic of the talk and you have paid attention (asking something the speaker explained 10 minutes earlier makes you look really stupid). However, it is usually better to avoid asking questions than forcing you to ask one.