Die Mitarbeiterin im Bürgeramt erklärt mir geduldig, welche Unterlagen ich noch brauche.

Mitarbeiterin means female employee/staff member. German often distinguishes masculine and feminine job titles:

• der Mitarbeiter = male employee
• die Mitarbeiterin = female employee

The ending -in is a very common way to make a feminine noun from a masculine one.

im is a contraction of in dem.

• in dem Bürgeramt → im Bürgeramt

Here it means in/at the citizens' office.

German often uses in with places, and when it combines with dem, it usually becomes im.
Because this is a location, dem is in the dative case.

Also note:

• das Bürgeramt = the citizens' office
• so dem Bürgeramt is the dative form of das Bürgeramt

Because the verb erklären normally works like this:

• jemandem etwas erklären = to explain something to someone

So the person receiving the explanation is in the dative case:

• mir = to me
• dir = to you
• ihm/ihr = to him/her

So:

• Die Mitarbeiterin erklärt mir ... = The employee explains ... to me

If you used mich, that would be accusative, and it would not fit the usual pattern of erklären here.

The thing being explained is the whole clause:

welche Unterlagen ich noch brauche

So the structure is:

• Die Mitarbeiterin = subject
• erklärt = verb
• mir = indirect object in the dative
• welche Unterlagen ich noch brauche = the content being explained

In English, this is similar to saying:

• She explains to me which documents I still need.

The clause acts like the thing being explained.

Because this is a subordinate clause introduced by welche.

In German, the conjugated verb usually goes to the end of a subordinate clause.

So:

• main clause: Die Mitarbeiterin erklärt mir geduldig ...
• subordinate clause: welche Unterlagen ich noch brauche

Inside that subordinate clause:

• ich = subject
• noch = adverb
• brauche = verb at the end

This is one of the most important word order patterns in German.

German normally uses a comma before a subordinate clause.

So the comma here is required because:

• welche Unterlagen ich noch brauche is a subordinate clause
• it depends on the main clause

German comma rules are often stricter than English ones, so learners need to get used to this.

Here welche Unterlagen means which documents.

• welche = which
• Unterlagen = documents / paperwork / required papers

In this sentence, the speaker already has some situation in mind, and the employee is explaining which specific documents are still needed.

It is accusative plural, because it is the object of brauche in the subordinate clause:

• ich brauche welche Unterlagen

However, in the plural, welche Unterlagen looks the same in the nominative and accusative, so you cannot tell just from the form alone. You tell from the role in the sentence.

• ich = subject
• welche Unterlagen = object

So it is accusative plural.

Here noch means something like still or yet.

So welche Unterlagen ich noch brauche means:

• which documents I still need
• which documents I need in addition
• which documents I haven't provided yet

This is a very common use of noch.

geduldig means patiently. It describes how the employee explains something.

In this sentence:

• Die Mitarbeiterin im Bürgeramt erklärt mir geduldig ...

This placement is natural and common.

Yes, adverbs like geduldig can sometimes move, but not every position sounds equally natural. For example:

• Die Mitarbeiterin erklärt mir geduldig, ... = very natural
• Geduldig erklärt mir die Mitarbeiterin, ... = possible, but more marked/emphatic
• Die Mitarbeiterin geduldig erklärt mir ... = not correct

So learners should usually keep it in a normal adverb position like the one in the sentence.

Yes, im Bürgeramt is giving more information about die Mitarbeiterin.

So it means:

• the employee at the citizens' office

It tells you which employee is meant. In practice, it functions like part of the larger description of the subject.

So the subject is not just die Mitarbeiterin, but more fully:

• Die Mitarbeiterin im Bürgeramt

That sounds unnatural. In German, pronouns like mir often come earlier than longer elements or adverbs.

So this is much better:

• Die Mitarbeiterin im Bürgeramt erklärt mir geduldig, ...

German word order is flexible, but it is not random. Short pronouns such as mir usually appear relatively early in the middle of the sentence.

Yes. die Unterlage can mean document or paper, but in real-life German, especially in office and bureaucracy contexts, people often use the plural Unterlagen to mean:

• documents
• paperwork
• supporting papers

This is extremely common when talking about forms, applications, official requirements, and similar situations.

Yes, you can think of it that way.

A direct question would be:

• Welche Unterlagen brauche ich noch?
  = Which documents do I still need?

In the sentence you were given, that question becomes embedded inside a larger sentence:

• Die Mitarbeiterin erklärt mir, welche Unterlagen ich noch brauche.

That is often called an indirect question or embedded question.
When German does this, the verb moves to the end of the clause.

Yes. brauchen is the standard everyday verb for to need.

So:

• ich brauche = I need
• du brauchst = you need
• wir brauchen = we need

In official contexts, it is very common:

• Ich brauche noch meinen Pass.
• Welche Unterlagen brauche ich?

So this is a very natural verb choice in the sentence.