For the difference こちら (kochira) and この人 (kono hito), the former is a politer version of the latter. In business settings, you should almost always be using こちら, especially when you are in front of that person. Using この人 can be even rude.
For the difference between どなた (donata) and どの人 (dono hito):
- どなた is a politer version of だれ (dare) or "who".
- どの人 is "which person". This is used when there are several people and you have to select one person among them.
You can combine these words arbitrarily to form a question.
こちらはどなたですか ("Kochira wa donata desu ka?") and この人はどなたですか ("Kono hito wa donata desu ka?") translate to "Who is this person?". This is a fairly simple question.
こちらはどの人ですか ("Kochira wa dono hito desu ka?") and この人はどの人ですか ("Konohito wa donohito desu ka?") translate to "Which person is this person?", but this is a rare question that makes sense only in rare contexts. This question makes sense, for example, when you are looking at an old photo of a baby of a certain family but you don't know which person of the family is in the photo.