Learn Hardcore Turkish: Yarın sınavın ne kadar zor olacağını bilmiyoruz. - We do not know how difficult tomorrow’s exam will be.

So Turkish word order is generally Subject–Object–Verb (SOV), not SVO like English. The whole clause sınavın ne kadar zor olacağını is the object of bilmiyoruz, so it naturally comes right before it.

Why is it sınavın and not just sınav?

Sınavın is in the genitive case (with the suffix -ın), and it’s part of a genitive–possessive construction used for noun clauses.

Pattern:
[noun in genitive] + [verb with possessive ending]

Here:

sınav-ın = of the exam / the exam’s
olacağ-ı = its being / the fact that it will be

Together, sınavın … olacağı literally feels like “the exam’s being (so) hard”.

So:

sınavın ne kadar zor olacağını ≈ “how hard the exam will be” (as a noun phrase, the object of bilmiyoruz).

If you used just sınav, the grammar of the noun clause would be incomplete.

What exactly is olacağını and how is it formed?

Olacağını comes from the verb olmak (to be / to become) and is a future-tense noun clause form.

Morphologically:

ol- – stem of olmak
-acak – future tense / future participle
-ı – 3rd person singular possessive ending
-nı – accusative case (object marking)

Spelled together with consonant change:
ol-acak-ı-nı → olacağını

Functionally, olacağını means “that it will be” as part of a noun clause:

zor olacağını = that it will be difficult / hard

The whole sınavın ne kadar zor olacağını is the thing we don’t know.

Why do we need olacağını at all? Why not just say ne kadar zor?

Ne kadar zor by itself is only an adjective phrase: how hard.

To use it as the object of a verb like bilmek (to know), Turkish normally needs a full noun clause built from a verb:

sınavın ne kadar zor olacağını – how hard the exam will be (full clause, can be object)
sınavın ne kadar zor – ungrammatical here as an object; it’s not turned into a noun clause

In English we can say:

We don’t know *how hard the exam will be.*

But in Turkish, the “will be” part (olacağını) is required to nominalize the clause so it can act as the object.

Why is there no word like “that” (e.g. ki) in this sentence?

English often uses that to introduce content clauses:
We don’t know that / how hard the exam will be.

Turkish usually does not need a separate word like that. Instead, it uses:

verb-based noun clause endings (like -acağ-ı here)
plus often a genitive on the subject of that clause (sınavın)

So sınavın ne kadar zor olacağını already grammatically marks “the fact of how hard the exam will be”.
You do not add ki here; ki is used in different, more limited structures (often in spoken/colloquial emphasis, or fixed expressions).

Why doesn’t the question word ne kadar make the whole sentence a question?

Because ne kadar is inside an indirect question (a noun clause), not forming a direct question.

Compare:

Yarın sınavın ne kadar zor olacağını bilmiyoruz.
We don’t know how hard the exam will be.
→ The whole sentence is a statement about our lack of knowledge.
Yarın sınav ne kadar zor olacak?
How hard will the exam be tomorrow?
→ This is a direct question; the verb is finite and the sentence ends with a question mark.

In the original sentence, ne kadar functions inside a noun clause (object of bilmiyoruz), so the main sentence is not a question; it’s just saying we don’t know something.

What does ne kadar contribute here exactly? Is it “how”, “how much”, or “how many”?

Ne kadar literally means “how much / how many”, but with adjectives it often means just “how (adjective)”:

ne kadar zor – how hard / how difficult
ne kadar güzel – how beautiful
ne kadar pahalı – how expensive

With quantities or amounts, it can mean “how much / how many”:

Ne kadar para var? – How much money is there?
Ne kadar öğrenci var? – How many students are there?

In your sentence, ne kadar zor = how hard / to what degree difficult.

Why is the tense different: olacağını (future) but bilmiyoruz (present)?

Each verb uses the tense that fits its own meaning:

bilmiyoruz – present continuous / general present: we (currently) don’t know
olacağını – future in the noun clause: (that) it will be

So the knowing (or not knowing) is about now, but it concerns an exam that is in the future. English does the same thing:

We *don’t know how hard the exam will be tomorrow.*

Could we use olduğunu instead of olacağını? What would change?

Yes, but the meaning changes:

olacağını – future: will be
olduğunu – non-past / factual: roughly is / was / (the fact that it is/was), depending on context

So:

Yarın sınavın ne kadar zor olacağını bilmiyoruz.
We don’t know how hard the exam will be tomorrow. (future)
Şu anda sınavın ne kadar zor olduğunu bilmiyoruz.
We don’t know how hard the exam is (right now / in general).

For an exam tomorrow, the future form olacağını is the natural choice.

Why is the subject biz (we) not stated? Can we say Biz bilmiyoruz?

In Turkish, personal endings on verbs usually make the subject optional:

bilmiyoruz already contains -uz, meaning we.
So adding biz is not necessary: biz bilmiyoruz and bilmiyoruz both mean we don’t know.

You can say Biz bilmiyoruz, but it adds emphasis:

Biz bilmiyoruz – We don’t know (maybe others do, or in contrast to someone else).

Can the position of yarın change, and does that change the meaning?

You have some flexibility, but word order can affect emphasis and sometimes naturalness.

Most natural here:

Yarın sınavın ne kadar zor olacağını bilmiyoruz.
Neutral, very natural: Tomorrow, we don’t know how hard the exam will be.

Other possibilities:

Sınavın ne kadar zor olacağını yarın bilmiyoruz.
This sounds odd or wrong; it suggests something like We don’t know tomorrow how hard the exam will be, which is not the intended meaning.
Sınavın yarın ne kadar zor olacağını bilmiyoruz.
Grammatical, but now yarın is inside the noun clause, emphasizing the time of the exam more strongly: We don’t know how hard the exam will be *tomorrow (as opposed to some other day).*

Placing yarın at the very beginning (Yarın … bilmiyoruz) is the most neutral and common here.

Why is the verb bilmiyoruz (with -yor) used instead of bilmeyiz?

Both exist, but they have different nuances:

bilmiyoruz – present continuous/general, very common for current states:
- Yarın sınavın ne kadar zor olacağını bilmiyoruz.
  We (currently) don’t know how hard the exam will be tomorrow.
bilmeyiz – aorist (habitual / general truth / prediction).
It can sound like:
- We generally don’t know / we are not likely to know / we wouldn’t know.

In this sentence, you are describing a current state of not knowing, so bilmiyoruz is the natural choice.