Appropriate topics over lunch with an invited speaker
There's always plenty of questions to ask. If you knew as much, or more than your speaker, you wouldn't need to ask it!

Questions that do not require a lot of experience in the field to be able to ask or understand and provide a higher volume of response. In addition, a lunch setting is less formal than a lecture, so you can use more open-ended questions not necessarily related to his talking point.

Here are some example questions that would apply to most fields.


What do you think is the most promising research in [the field] you've seen recently?
How did you come up with the idea behind [topic]?
Can you explain the [concept] as it was related to [the paper]?
I am a member of the [department] which is similar to your field. What have you seen in interdisciplinary topics that you find interesting?


With a specific field, you can also ask the speaker his opinion on [new concept XYZ] that you've learned about or read about.

Questions I've seen that are more "awkward" typically involve accidentally eliciting a direct yes/no answer along the way. Avoid "Do you think..." in favor of "Why do you think..."