When the speaker stops to take questions
The moment when the speaker says "any questions so far?" is a good time to clarify larger ideas you're confused about, or ask for a more detailed explanation of something, or ask about something you're interested in.
Some good all-purpose question phrases
"I was wondering, _____?"
"I'm curious, ______?"
"Do you mind explaining _____?
"Do you mind clarifying _____?
Directly the speaker's attention to a specific point
"There's one thing I'm confused about: ______?"
"There's one thing I'm curious about: ______?"
"I was just wondering if you could clarify one thing: _____?"
"There's one thing I'm still a little foggy about: ____?"
Asking the speaker to expand on, elaborate, or clarify something:
"Do you mind saying more about _____?"
"Do you mind talking more about _____? I'm curious to know, ____?"
"When you say _____, do you mean ______?"
"So are you saying that _____?"
"So does that mean _____?"
"I'm just curious, ______" (for asking a question not totally related to the main point)
for example, "So I'm just curious, what's your personal opinion about whether religious rituals should be allowed in schools?"
Referring back to something in the past:
"Back when you were talking about ____, ______ ?"
"Back when you mentioned _____, _____?"
... did you mean _____?"
... were you referring to ____?"
... what did you mean by _____?"
- (for example: "Back when you were talking about Socrates and the oracle, what did you mean when you said the prophecy was ambiguous? I'm still a bit foggy about that.")
"Sorry, could you go back and explain _____ in more depth? I'm still not totally clear on that point."
"Sorry, I didn't follow that last part about ____. Do you mind...?" (explaining, clarifying, repeating, etc)
"... that thing you said earlier about _____"
"... that point you made earlier about ____"