Are you asking about the use of "you all" in this question? If so, in the US, it depends on the region of the country. In the South, "you all" just means "you", so you could be asking one or many people the question. In most of the rest of the country, "you all" suggests you are asking multiple people at the same time. A performer often greets the audience with, "How are you all doing today?" referring to each person in the audience.

"How are you today? / How are you doing today?" They're both the same. and in your sentence, you ask PEOPLE. It's plural.