When the verb "savoir" is for a knowledge, when it means that you know "how to do something", you remove the "how" ("comment"). For example, "tu sais nager" instead of "tu sais comment nager".
To say this another way: never use 《 comment 》 directly after 《 savoir 》.
Where is the "how" in this sentence?
It's implied sort of. You don't have to add "comment". In fact I think that would be incorrect.
That is what I am asking? There went my first heart ...
why is it not "parfait(e)s" when there is "vous"
Maybe they're talking to a single person in a formal way?
Peut-être. Merci :-)
Would there be any difference in pronunciation, if someone was to say "Vous avez être parfait !"? Does this sentence even make sense?
I don't believe that sentence makes sense, but the pronunciation would be different, if I'm not mistaken. Vous savez (voo Sah vay); Vous avez (voo Zah vay)
I'm guessing your question stems from the English phrase "You have to be perfect!" French wouldn't use have like that; they'd likely say, "Vous devez être..." etc. You must be.
The translation here and the translation there are two different things. When I did the exercise the phrase translated to 'You know being perfect' which is an incomplete sentence or bad grammar, or both.