Learn Hardcore German: In der Biografie steht, wie viele Rückschläge der Musiker erlebt hat. - In the biography it says how many setbacks the musician experienced.

In der Biografie steht … ≈ “In the biography it says …” / “The biography states …”
ist would literally mean “is,” and In der Biografie ist … would usually refer to a physical object being located in/on the biography (which makes no sense here).

So stehen here is a set expression for information that is written somewhere:
Im Vertrag steht, dass … – “The contract says that …”
Auf dem Schild steht … – “The sign says …”

What case is der Biografie, and why?

Der Biografie is dative singular.

The noun Biografie is feminine: die Biografie.
The preposition in can take either dative (location) or accusative (movement).
Here it’s a location (“in the biography” as a place where something is written), so you use dative:
- in der Biografie = in + die Biografie → der Biografie (feminine dative singular)

So: In der Biografie literally: “in the biography (as a location)”.

What is the subject of the main clause In der Biografie steht, …?

The subject of the main clause is the whole subordinate clause:

wie viele Rückschläge der Musiker erlebt hat

So structurally, it’s:

In der Biografie – prepositional phrase (fronted)
steht – finite verb
wie viele Rückschläge der Musiker erlebt hat – clause functioning as the subject

If you put the subject clause at the beginning, you can see it more clearly:

Wie viele Rückschläge der Musiker erlebt hat, steht in der Biografie.

Same meaning, just a different word order that makes the grammar more visible.

Why is there a comma before wie?

The comma marks the start of a subordinate clause.

wie viele Rückschläge der Musiker erlebt hat is an indirect question clause introduced by wie.
In German, all subordinate clauses (Nebensätze) are separated from the main clause by a comma.

So the comma is obligatory:
In der Biografie steht, wie viele Rückschläge der Musiker erlebt hat.

What exactly does wie mean here?

Here wie introduces an indirect question about an amount: “how many”.

wie viele = “how many”
The whole clause wie viele Rückschläge der Musiker erlebt hat means “how many setbacks the musician has experienced.”

This is not a comparison (“as/like”) but the question-word use of wie (“how”).

Why is it wie viele and not wieviele?

Modern standard spelling is two words: wie viele.

wie = how
viele = many (plural form of viel used with countable nouns)

You only use wie viel or wie viele (two words), depending on whether the noun is countable:

wie viel Zeit – how much time (uncountable)
wie viele Rückschläge – how many setbacks (countable, plural)

Older or non‑standard spelling wieviel(e) is mostly avoided in contemporary standard German.

Why is the verb order der Musiker erlebt hat and not hat der Musiker erlebt?

Because this is a subordinate clause.

In German subordinate clauses (introduced by wie, dass, weil, etc.):

The finite verb (here: hat) goes to the end of the clause.
Any other verb forms (here: erlebt, the past participle) come just before the finite verb.

So:

Main clause: Der Musiker hat viele Rückschläge erlebt. (verb in second position)
Subordinate clause: … wie viele Rückschläge der Musiker erlebt hat. (finite verb last)

Why is it erlebt hat and not hat erlebt at the end?

In subordinate clauses with more than one verb:

The non-finite verb forms (infinitive or past participle) come first.
The finite (conjugated) verb comes last.

Here:

erlebt is the past participle of erleben.
hat is the finite auxiliary (3rd person singular).

So the correct order in a subordinate clause is:

… der Musiker erlebt hat

not *hat erlebt at the end.

What tense is erlebt hat, and why is it used here?

Erlebt hat is the present perfect tense (Perfekt):

Auxiliary: hat (haben)
Past participle: erlebt

In spoken and much written German, Perfekt is frequently used to talk about completed past actions, especially in narratives:

Der Musiker hat viele Rückschläge erlebt. – “The musician has experienced / experienced many setbacks.”

Here, it describes setbacks that happened before the time of writing and are now part of his life story.

What case is der Musiker, and why is it der and not den or dem?

Der Musiker here is nominative singular, masculine.

Inside the subordinate clause … der Musiker erlebt hat:

der Musiker is the subject – the one who experienced the setbacks.
Subjects take the nominative case.
The noun Musiker is masculine: nominative singular article = der.

So:

Nominative: der Musiker (subject)
Accusative: den Musiker
Dative: dem Musiker

You use der because of the nominative subject role.

Why is Rückschläge plural, and how is its plural formed?

Rückschlag (singular) = “setback”
Rückschläge (plural) = “setbacks”

Plural formation:

Base noun: der Rückschlag
Plural: die Rückschläge
- Add -e
- Add Umlaut to the vowel a → ä

So:

singular: ein Rückschlag
plural: viele Rückschläge

The sentence talks about more than one setback, so the plural is needed, and wie viele also signals a plural count.

What is the difference between Biografie and Biographie?

They are the same word, just different spellings:

Biografie – recommended modern spelling (after the German spelling reform)
Biographie – older / traditional spelling, still understood but less common in current standard usage

Both mean “biography.” In modern texts, Biografie is preferred.

Can we change the word order to start with the wie‑clause?

Yes. You can say:

Wie viele Rückschläge der Musiker erlebt hat, steht in der Biografie.

This is fully correct and means the same thing.
Differences:

Original: focuses first on where the information is found (In der Biografie …).
Reordered: focuses first on what the information is about (Wie viele Rückschläge …).

Can we add es and say Es steht in der Biografie, wie …?

Yes, that is also possible:

Es steht in der Biografie, wie viele Rückschläge der Musiker erlebt hat.

Here es is a dummy (expletive) subject. The real (content) subject is still the clause wie viele Rückschläge ….

German often omits this dummy es when the clause functioning as subject is placed at the end, but including it is also grammatical and common in speech and writing.