I think "How does one find him?" is a general sentence, then the absolute pronoun would be used in Vietnamese (this is not included in the course, and there are much many more pronouns):
The absolute pronoun người ta has a wider range of reference as "they, people in general, (generic) one, we, someone".
(Then, would you prefer the expression in this lesson not to be included? This expression is very simple to translate to Spanish as ¿Cómo encontrarle/encontrarlo?, and a good interpreter would translate the sentence with người ta as ¿Cómo lo/le encuentra la gente -a él-? or ¿Cómo se lo encuentra?, I think the latter is much better.)
one (used as French on) = người ta
(I hope it helps.) ;)
From Wikipedia: https://en.wikipedia.org/wiki/Vietnamese_pronouns
No question about the Vietnamese but throughout the course the English needs to be correct as well. The point that the Vietnamese can be shortened is well taken but the subject, whether "you" as N. Americans would say or "one" as Brits would say, cannot be excluded. Better to deal with this point in the opening notes.
Having looked at the other posts here, it seems to me that this is an example of a sentence that needs to be rendered with a different structure in English. "How to find him" is a conceivable question in English, but it is almost intolerably awkward in most situations. "How does one find him" or "How would one find him" are better English sentences.