Könnten Sie mir bitte erklären, wieso das Pronomen hier vor dem Verb steht?

Because this is a polite question/request, and in German yes/no questions normally put the finite verb first.

So:

• Sie könnten mir ... erklären. = You could explain ... to me.
• Könnten Sie mir ... erklären? = Could you explain ... to me?

This is normal German word order for a direct question.

Könnten Sie ... ? sounds more polite and less direct than Können Sie ... ?

Compare:

• Können Sie mir das erklären? = Can you explain that to me?
• Könnten Sie mir das erklären? = Could you explain that to me?

So könnten is often used to soften a request, much like English could.

Because Sie here is the formal word for you.

German distinguishes:

• du = informal singular you
• ihr = informal plural you
• Sie = formal you (singular or plural)

The formal Sie is always capitalized, which helps distinguish it from sie meaning she or they.

Because the verb erklären usually works with:

• jemandem etwas erklären = to explain something to someone

That means:

• the person gets the dative case
• the thing being explained gets the accusative case

So:

• mir = dative of ich
• mich = accusative of ich

In this sentence, the speaker is the person receiving the explanation, so German uses mir.

Because Könnten is a modal verb, and in German modal verbs send the main verb to the end of the clause in its infinitive form.

So the structure is:

• Könnten = finite modal verb
• Sie mir bitte ... erklären = rest of the clause, with erklären at the end

This is standard German word order with modal verbs:

• Ich kann das erklären.
• Kannst du das erklären?
• Könnten Sie mir das erklären?

Because wieso introduces a subordinate clause here:

• ..., wieso das Pronomen hier vor dem Verb steht

In German, subordinate clauses are normally separated from the main clause by a comma. So the comma is required.

Because wieso introduces a subordinate clause, and in German subordinate clauses usually send the finite verb to the end.

Compare:

• Main clause: Das Pronomen steht hier vor dem Verb.
• With wieso: ..., wieso das Pronomen hier vor dem Verb steht.

That verb-final pattern is one of the most important features of German subordinate clauses.

Because once wieso starts the subordinate clause, German no longer uses normal main-clause question order. Instead, it uses subordinate-clause word order, where the verb goes to the end.

So:

• Main clause question: Wieso steht das Pronomen hier vor dem Verb?
• Embedded/subordinate clause: ..., wieso das Pronomen hier vor dem Verb steht

In the subordinate clause, das Pronomen is the subject, and the finite verb steht must come at the end. So the subject naturally appears before the verb.

In this sentence, yes, pretty much.

You could also say:

• Könnten Sie mir bitte erklären, warum das Pronomen hier vor dem Verb steht?
• ... weshalb ...

All three can mean why. The differences are mostly about style and tone:

• warum = very common, neutral
• wieso = also common, sometimes a bit more conversational
• weshalb = slightly more formal or written

But grammatically, they work the same way here.

Here hier means something like here / in this case / in this sentence.

It does not necessarily mean a physical place. Instead, it points to the specific example being discussed:

• wieso das Pronomen hier vor dem Verb steht
• roughly: why the pronoun is here / in this instance before the verb

So hier refers to the word order in the example under discussion.

Because vor can take either dative or accusative, depending on meaning:

• dative for location/static position
• accusative for movement toward something

Here the meaning is static position: the pronoun is located before the verb, not moving there. So German uses the dative:

• vor dem Verb

If it were movement, accusative could appear in other contexts, but not here.

Yes. That would be completely correct.

You could replace wieso with:

• warum
• weshalb

without changing the basic grammar. The subordinate clause would still keep the verb at the end:

• ..., warum das Pronomen hier vor dem Verb steht
• ..., weshalb das Pronomen hier vor dem Verb steht

Yes. That is also correct.

The difference is mainly politeness/tone:

• Können Sie ... ? = polite
• Könnten Sie ... ? = a little softer and more polite

So the original version sounds especially courteous, which is common when asking for an explanation.