The actress Sandra Oh is one of the first persons to come to mind, when I think of how to answer questions on the spot.

She never hesitates to give herself a few seconds to ponder the question and give an answer, and she comes off as being highly reflective, thoughtful, and intelligent.

Here's an example of her taking a thoughtful pause: https://youtu.be/MaGAY_uMmcQ?t=1222 She does it throughout the video, but this particular example is a notable one.