I understand that 'všude' means 'everywhere', but 'anywhere' is used in negative statements such as this one.
Not in this case! This sentence states, that while he is known in some places, there are places where they don't know him, hence the "everywhere". ;)
"They don't know him anywhere." translates to "Nikde ho neznají."
Yes but this is not something that is really said in English. It would almost always be phrased differently since it doesn't make any practical sense in English. How do you know someone somewhere but not everywhere? Perhaps you don't recognize him but again, "known" in English has a more thorough meaning than 'recognize', and therefore would not be used in this way by a native speaker.
Is such a saying used often in Czech?
As a native speaker, I disagree. The example uses "they know," not "you know" or "one knows." The sentence literally says "They do not know him/it everywhere." Do they know him in Paris? Yes. In Berlin? Yes. In Prague? No. Well then, I guess they do not know him everywhere.
This reminds me of something... "I would not eat them in a box, I would not eat them with a fox, I would not eat them here or there, I would not eat them anywhere!"
Nope, it isn't. I'd say it's there just to show the differences between VŠUDE/NIKDE. :)
I wrote "He isnt known everywhere" and the corrected option that was written was- they dont know IT everywhere. It is wrong right?
That's weird. "Ho" can also mean "it", because in Czech objects have genders too, for example, "Vidím hrad. Vidíš ho?" It's still weird if that answer can also be used.
actually, ho is the accusative of both on AND ono. ono is the other neuter pronoun available in czech, even if less frequently used than the demonstrative-ish to. there are contexts in which to just does not cut it and a form of ono is necessary.
Toto slovo lze v češtině použít i pro střední rod, ale mnoho lidí ___ používá jen pro rod mužský.
je, jej, and ho work fine here in the order of decreasing formality, while to would cross into the rather uneducated zone. (but then again, look who we just elected to second term.)
you may want to refer to the tips/notes provided with the Pronouns skill:
Several forms (e.g., ho, je/ně, and jej/něj) appear in more than one row of the table. Their meaning depends on context.