Η ασθενής είπε ότι έχει ακόμα πόνο στο γόνατο.

Not all feminine nouns follow that pattern. Ασθενής is an adjective/noun with the ending -ής, and in the singular nominative it has the same form for masculine and feminine.

So:

• ο ασθενής = the male patient
• η ασθενής = the female patient

The article tells you the gender here.

Also, ασθενής originally means sick / ill, but it is very commonly used as a noun meaning patient.

Greek usually uses the definite article much more often than English does. So η ασθενής is the normal way to say the patient.

You can sometimes omit the article in certain styles, especially in headlines, notes, or very formal/telegraphic contexts, but in ordinary full sentences, η ασθενής είπε sounds much more natural than just ασθενής είπε.

Είπε is the aorist form of λέω (to say). In this sentence it means said.

So:

• λέει = he/she says / is saying
• είπε = he/she said

The aorist is very commonly used for a completed past action, like reporting what someone said once.

Ότι means that and introduces a content clause, just like English that in she said that...

So:

• είπε ότι έχει πόνο = she said that she has pain

In everyday Greek, πως can often be used in the same way:

• είπε πως έχει πόνο

Both are common here.

Because Greek does not have to shift the tense backward the way English often does.

English often says:

• She said that she still had pain

But Greek can keep the verb in the present if the pain is still true at the time being referred to:

• είπε ότι έχει ακόμα πόνο

This suggests the pain is ongoing. If you used a past form, it could suggest the pain belonged more clearly to the past.

So Greek is often more direct about the actual time of the situation, rather than automatically changing the tense after a past reporting verb.

Here ακόμα means still.

So έχει ακόμα πόνο means still has pain.

Depending on context, ακόμα can also mean yet or even, but in this sentence still is the natural meaning.

Its position is flexible, but here it sits naturally before πόνο:

• έχει ακόμα πόνο

You may also hear:

• ακόμα έχει πόνο

Both are possible, though the nuance/focus may shift slightly.

Because πόνο is the accusative singular, and it is the direct object of έχει.

The base form is:

• ο πόνος = the pain

But after έχει (has), Greek uses the accusative:

• έχει πόνο = has pain

So:

• nominative: ο πόνος
• accusative: τον πόνο / πόνο

This is very normal after verbs that take a direct object.

Because Greek often omits the article when speaking generally about a condition or symptom.

• έχει πόνο = has pain
• έχει πυρετό = has a fever
• έχει βήχα = has a cough

Using τον πόνο would usually sound more specific, as if referring to a particular pain already identified in the conversation. In this sentence, πόνο without the article is the natural general way to describe the symptom.

Στο is a contraction of:

• σε + το = στο

Here σε means something like in / at / on, depending on context, and το is the neuter singular definite article.

So:

• στο γόνατο = in the knee / at the knee

This contraction is extremely common:

• σε + τον = στον
• σε + τη(ν) = στη(ν)
• σε + το = στο

Greek often omits the possessive with body parts when it is obvious whose body part is meant.

So:

• πονάει το κεφάλι = my/his/her head hurts, depending on context
• έχει πόνο στο γόνατο = has pain in the knee

Since the subject is the patient, it is naturally understood as her knee.

If you want to make it explicit, you can say:

• στο γόνατό της = in her knee

Both are possible, but the version without the possessive is very natural.

Because γόνατο is a neuter noun in Greek.

Its basic form is:

• το γόνατο = the knee

So after σε + το, you get:

• στο γόνατο

This is just a matter of noun gender, which has to be learned with each noun.

It can do both.

As an adjective, ασθενής can mean:

• weak
• sick
• ill

As a noun, it commonly means:

• patient

In your sentence, because it has the article η and refers to a person in a medical context, it clearly means the patient.

Yes. Greek often expresses this idea in more than one natural way.

For example:

• Η ασθενής είπε ότι πονάει ακόμα το γόνατό της.
• Η ασθενής είπε ότι έχει ακόμα πόνο στο γόνατο.

The version with έχει πόνο sounds a bit more clinical or medical, while πονάει is often a more everyday way to say that something hurts.

Both are correct; the original sentence sounds very natural in a medical setting.