I'm wondering either why ještě is necessary or why the English translation doesn't read 'He hasn't yet been anywhere at all.'
I don't get what you are wondering about, because it is NOT necessary. It is perfectly accepted without it.
It is sort of implied by the English perfect tense and therefore the preferred translation does contain it.
Hmmm...I think I submitted vůbec nikde nebyl and was marked incorrect. However, I'll check it out again when I'm working on the advance to the next level. Thanks for the timely response! Your comments are really helpful!