This doesn't make too much sense in English...are they asking "who is this inquiry coming from?" or "where is this inquiry coming from" (as in "who referred you to us"? It either means "reason for your inquiry"/"why do you wish to learn more about us?" or "who sent/referred you to us" (similar to "how did you find out about us". The translation I propose is vague enough to match the English...but it's probably best to specify based on what they are *really* asking.