Learn German: Wir besuchen das Gebiet, woher das kulturelle Lehnwort stammt. - We are visiting the region where the cultural loanword originates from.

woher indicates origin or movement away from a place ('from where'). Because the verb stammen means 'to originate' or 'to come from', it requires this sense of origin. If you used wo, it would just mean 'where', which doesn't match the idea of a word originating from a region.

How does woher affect the word order in the second half of the sentence?

Like other relative pronouns, woher introduces a subordinate clause. This means it kicks the conjugated verb, which is stammt here, all the way to the very end of the sentence.

Why is the adjective ending in das kulturelle just -e? Doesn't a neuter word usually need an -s?

The definite article das already does the heavy lifting of showing us that Lehnwort is a neuter noun. Because the article already clearly shows the gender and case (nominative subject), the adjective just gets the 'weak' ending, which is -e.

I know kommen means 'to come'. How is stammen different here?

While you could absolutely say woher das Wort kommt, stammen is a bit more specific and formal. It means 'to originate' or 'to be derived from.' It is mostly used for things with historical, cultural, or geographical roots, making it the perfect verb to pair with a loanword.