Use whichever word best applies to the translation. I am told that the Dutch don't conceptualize "anywhere", "anybody" and "anyone" quite the way that English-speakers do. These concepts are best explained with a phrase (such as waar dan ook in the case of "anywhere"), rather than depending upon a single word. But if "anywhere" applies to the overall sentence containing ergens, then use it.
But it doesn't fit here.
it comes probably from the same root as the following German words: irgendwo (whereever, anywhere), irgendjemand(somebody), irgendwann (anytime). The root word irgend kann be used also to show "just any", like irgend ein Apfel (any apple). So I think the Dutch word ergens and the German irgend has a common root.