Teşhis klinikte açıklandı.

Because Turkish adds the locative case to show location, meaning in / at.

• klinik = clinic
• -de / -da / -te / -ta = in / at

Here, klinik + -te = klinikte = at the clinic / in the clinic.

Why -te and not -de?

• The final consonant in klinik is k, which is voiceless
• After a voiceless consonant, Turkish usually uses t instead of d

So:

• evde = at home
• okulda = at school
• parkta = in the park
• klinikte = at the clinic

Açıklandı is a past tense passive verb.

It comes from:

• açıklamak = to explain, announce, disclose
• açıklanmak = to be explained, to be announced
• açıklandı = was explained / was announced

You can think of it like this:

• açıkla- = explain
• -n- = passive marker here
• -dı = past tense

So açıklandı means that something happened in the past, and the sentence does not focus on who did it.

Turkish often uses the passive when the doer is unknown, unimportant, or simply not mentioned.

So:

• Teşhis klinikte açıklandı. = The diagnosis was explained/announced at the clinic.
• Doktor teşhisi klinikte açıkladı. = The doctor explained the diagnosis at the clinic.

In the passive sentence, the speaker cares more about the diagnosis and where it was explained, not about who explained it.

If you want to mention the doer in a passive sentence, Turkish can use tarafından:

• Teşhis doktor tarafından klinikte açıklandı.
• The diagnosis was explained at the clinic by the doctor.

The difference is passive vs active.

• açıkladı = he/she/it explained
• açıklandı = it was explained

Examples:

• Doktor teşhisi açıkladı.
  The doctor explained the diagnosis.

• Teşhis açıklandı.
  The diagnosis was explained.

So in your sentence, açıklandı tells you that teşhis is not the doer. It is the thing being explained.

Yes, in this sentence teşhis is the grammatical subject of the passive verb.

That may feel a little strange to an English speaker because in meaning it is the thing receiving the action. But in passive sentences, that is normal:

• The doctor explained the diagnosis.
  Here the doctor is the subject.

• The diagnosis was explained.
  Here the diagnosis becomes the subject.

In Turkish:

• Doktor teşhisi açıkladı.
  teşhisi is object, marked with accusative -i

• Teşhis açıklandı.
  teşhis is now the subject, with no accusative ending

Because it is in the basic form here, often called the nominative form.

Turkish nouns do not always need an extra ending. Endings are added only when grammar requires them.

Compare:

• teşhis = diagnosis
• teşhisi = the diagnosis, as a definite object
• teşhiste = in the diagnosis
• teşhisten = from the diagnosis

In Teşhis klinikte açıklandı, teşhis is the subject of a passive sentence, so the plain form is correct.

Because Turkish normally puts the finite verb at the end of the sentence.

A very common Turkish sentence pattern is:

• Subject + other information + verb

So:

• Teşhis = subject
• klinikte = place
• açıklandı = verb

This end position for the verb is one of the most important word-order habits in Turkish.

Yes, Turkish word order is flexible, but changing it changes the focus or emphasis.

These are all possible:

• Teşhis klinikte açıklandı.
• Klinikte teşhis açıklandı.
• Açıklandı teşhis klinikte. — possible in special contexts, but much less neutral

The most neutral version is usually the one with the verb at the end.
Your sentence sounds natural and standard.

A rough idea of emphasis:

• Teşhis klinikte açıklandı. → neutral
• Klinikte teşhis açıklandı. → emphasizes where
• putting unusual things before or after can sound dramatic, poetic, or highly contrastive

Not with an article the way English does.

Turkish has no direct equivalent of the and usually no mandatory equivalent of a/an in sentences like this.

So teşhis can mean:

• the diagnosis
• a diagnosis

The exact meaning depends on context.

In many real situations, this sentence would naturally be understood as the diagnosis was explained/announced at the clinic, because the context probably already makes the diagnosis specific.

If Turkish really wants to stress one diagnosis / a diagnosis, it can use bir:

• Bir teşhis klinikte açıklandı.

But that is a different nuance and is not always natural in context.

No. Teşhis can mean different but related things depending on context:

• diagnosis in a medical context
• identification / recognition in other contexts

Because the sentence includes klinikte (at the clinic), the medical meaning diagnosis is the natural one here.

So the location helps you choose the correct meaning.

It can mean any of those, depending on context.

The verb açıklamak has a wider range than just one English word. It can mean:

• to explain
• to announce
• to make clear
• to disclose

So açıklandı can be:

• was explained
• was announced
• was disclosed

In a medical setting, both was explained and was announced can work, but was explained may sound more natural if a doctor is telling a patient about the diagnosis.

A simple pronunciation guide is:

Teşhis klinikte açıklandı
tesh-his kli-nik-te a-chuk-lan-duh

A few useful sound notes:

• ş sounds like sh
• ç sounds like ch
• ı is the Turkish vowel with no exact English equivalent; it is a dull, relaxed vowel, somewhat like the second vowel in sofa, but farther back
• teşhis sounds roughly like tesh-his
• açıklandı sounds roughly like a-chuk-lan-duh

You do not need a perfect accent right away; the most important thing is recognizing ş = sh, ç = ch, and the final verb shape.

Yes. The locative -de/-da/-te/-ta often covers both in and at in English.

So klinikte can be translated as:

• in the clinic
• at the clinic

English chooses between them based on what sounds more natural in context. Turkish does not make that distinction here.