You could compare it to the way the letter "k" behaves in English. Sometimes it's silent, e.g., know, knife, and sometimes it's not, e.g., keep, kernel.
In Norwegian, when "h" comes before a "v", it's silent, e.g., hvor, hvem, hvorfor, hvilke. It's also silent when it comes before a "j", e.g., hjemme, hjelpe (the "j" sounds like a "y" as in yam).
Duolingos aim is to try and help you understand and speak languages fluently. When you think of a language, your goal should be to think of them almost interchangeably. Thinking of 'Hvor bor han' as 'Where lives he' defeats the purpose, because it is not the correct order. You would never say 'Where lives he' unless you were going for a sort of archaic impression.