The first คน is the noun "person" and the second คน is the classifier for "person," which happens to be the same word. In English, it would be "the person there" (with นั้น for "there). As Piyah Phong said, there is a slight pause between a noun and its classifier.

คนคนนั้น ใช้เวลาจะเน้นว่าเค้าคือคนนั้น ให้ความรู้สึกมากกว่า คนนั้น

If you pause between the 2 words, you will understand that it means that person. I hope it is correct. I only learnt , my first language until 9 years. I don't think it is a new vocabulary.