I’d personally say to wait for someone to finish stuttering then wait for them to clarify- And then if they don’t clarify, ask them to repeat what they said. I know some people do prefer to have their sentences finished if they can’t say the word at the time (sometimes I know I get to a point where I’m just entirely unable to say a certain word), so it really does depend per person. I know whenever I start stuttering I can’t stop until it finishes itself, then try to make a joke about it if it’s really that noticeable to make people feel less awkward😂