"How is the soup cooked" translates most directly to "Xúp nầy nấu như thế nào?" for "this" soup and "Xúp đó nấu như thế nào?" for "that" soup, both of which work fine. As in English there are many ways to ask for this information and this way is well spoken, if direct. (In my experience, Vietnamese people are more likely to ask that you agree to personally teach them how /let them watch you make the dish at some point in the future than ask you directly how it is made, and most likely of all is that they will simply ask you for the recipe.)
I think the absolute pronoun would be used for general sentences (this is not included in the course, instead bạn is used for general conversations but there are many other pronouns for first, second and third person):
The absolute pronoun người ta has a wider range of reference as "they, people in general, (generic) one, we, someone".
Other terms can be used as pronouns:
In Vietnamese, virtually any noun used for a person can be used as a pronoun. These terms usually don't serve multiple roles like kinship terms (i.e. the term has only one grammatical person meaning). Words such as "doctor", "teacher", "owner", etc. can be used as a second-person personal pronoun when necessary.
And I would like to add the following expressions to show for example, how names are used as pronouns:
Vietnamese speakers also refer to themselves and others by name where it would be strange if used in English, eliminating the need for personal pronouns altogether. For example, consider the following conversation:
John: Mary đang làm gì vậy?
Mary: Mary đang gọi Joe. John có biết Joe ở đâu không?
John: Không, John không biết Joe ở đâu hết.
Directly translated into English, the conversation would run thus:
John: What is Mary doing?
Mary: Mary is calling Joe. Does John know where Joe is?
John: No, John doesn't know where Joe is.
A normal translation of the conversation into English would be:
John: What are you doing?
Mary: I am calling Joe. Do you know where he is?
John: No, I don't know where he is.
While always referring to oneself or the audience by name would be considered strange in English, in Vietnamese it is considered friendly, and is the preferred way to converse among close friends (however, in a kinship context, people with a lower rank cannot address their superiors by name).
From Wikipedia: https://en.wikipedia.org/wiki/Vietnamese_pronouns