Is there a way show a pause after one question (to show that the answer is being considered by the askER) before the second guestion is asked? Or is that too a matter for the narrative?
Yes. Do it in the narrative. In fact, there is a term for an action separating dialogue fragments. It's called a beat. Jack shoved Spike against the wall. "Where were you last night?" Then it dawned on him. "It was you who broke into the garage, wasn't it?"
if a pause/self-interruption is only within the line of dialogue and not accompanied by action, that's shown by inserting an ellipsis: "Last night...it was you who broke into the garage, wasn't it?"
