How did you find the seminar?
I will assume that you are curious as to how best to respond to such a question...
Such a question is often asked as part of a feedback form at the end of a seminar.
If it is being used properly, then it is probably intended to help identify how well the material is conveyed.
- Did the presenter engage well with the attendees?
- Did the presentation capture attention by making the material understandable and fun?
- Were attendees distracted from the important material by the things added to the presentation to make it more fun?
An arguably slightly improper usage is that the presenter wants to be encouraged by being told that you liked what they did.
It seems to me that it would be most helpful to engage the presenter with your response by being polite and saying what you did enjoy and how that was helpful, followed by what you found less enjoyable or difficult to understand. Try to give the presenter information that might help them present more effectively in future, without being directive.
Remember that it was not just to you that they were presenting and your experience will differ from that of other attendees. Take responsibility for your own part too.
For example, you might say something like:
I found the seminar on the history of radio fairly interesting. Einstein's joke (*) about the cat was fun and will probably help me remember that part of the talk. I got lost a little in some of the later technical details. It would probably have helped me if you had gone a little slower on that part, but perhaps that's just me.
(*) Einstein is (falsely) credited with explaining radio like this:
"You see, wire telegraph is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat."
(From the "fortune" program (1985))