Die Ärztin sagt, mein Daumen sei nur leicht verletzt, aber den Ellbogen solle ich zwei Tage schonen.

Ärztin is the feminine form of Arzt.

• der Arzt = male doctor
• die Ärztin = female doctor

German often forms feminine job titles with -in:

• der Lehrer → die Lehrerin
• der Student → die Studentin

Also, Ärztin is capitalized because all German nouns are capitalized.

They are forms of Konjunktiv I, which is commonly used for indirect speech or reported speech.

So instead of stating the doctor’s words as plain fact, the speaker is reporting them:

• mein Daumen ist nur leicht verletzt = my thumb is only slightly injured
• mein Daumen sei nur leicht verletzt = my thumb is only slightly injured, according to what the doctor says

Likewise:

• ich soll den Ellbogen zwei Tage schonen = I should rest the elbow for two days
• den Ellbogen solle ich zwei Tage schonen = the doctor says I should rest the elbow for two days

This is especially common in formal written German and journalism. In everyday spoken German, many people would simply use the indicative:

• Die Ärztin sagt, mein Daumen ist nur leicht verletzt, aber ich soll den Ellbogen zwei Tage schonen.

If the doctor were speaking directly to the patient, it would be something like:

Ihr Daumen ist nur leicht verletzt, aber den Ellbogen sollen Sie zwei Tage schonen.

or more neutrally:

Ihr Daumen ist nur leicht verletzt, aber Sie sollen den Ellbogen zwei Tage schonen.

When the patient reports this later, the pronouns change:

• Ihr → mein
• Sie → ich

So direct speech becomes indirect speech:

• direct: Ihr Daumen ... Sie sollen ...
• reported: mein Daumen sei ... ich solle ...

German can introduce reported speech in two common ways:

1. with dass
2. without dass

So both are possible.

Without dass:

• Die Ärztin sagt, mein Daumen sei nur leicht verletzt ...

With dass:

• Die Ärztin sagt, dass mein Daumen nur leicht verletzt sei ...

The version without dass is quite natural, especially in reported-speech style. It can sound a bit more formal or literary than plain everyday speech.

Also notice the word order difference:

• without dass: the clause keeps normal finite-verb position
• with dass: the finite verb goes to the end

This is because den Ellbogen has been moved to the front for emphasis or topic.

The more basic order would be:

..., aber ich solle den Ellbogen zwei Tage schonen.

But German often moves an element to the first position in the clause. When that happens, the finite verb still has to stay in second position:

• first position: den Ellbogen
• second position: solle
• then the subject: ich

So:

den Ellbogen solle ich zwei Tage schonen

This is a normal German word-order pattern, not a different meaning. It just gives extra focus to the elbow.

den Ellbogen is accusative, because it is the direct object of schonen.

The verb schonen takes an accusative object:

• den Arm schonen
• das Knie schonen
• den Ellbogen schonen

Since Ellbogen is masculine, the accusative singular article is den:

• nominative: der Ellbogen
• accusative: den Ellbogen

So here:

• ich = subject
• den Ellbogen = direct object

This is a very common difference between English and German.

German often uses the definite article with body parts where English prefers a possessive:

• English: rest your arm
• German: den Arm schonen

So den Ellbogen is very natural.

Using meinen Ellbogen would also be possible, but it is less idiomatic here because the owner is already obvious from context.

By contrast, mein Daumen is used because the speaker is explicitly identifying the thumb as my thumb in the reported statement. It sounds natural to keep the possessive there.

So the contrast is not strange in German:

• mein Daumen
• den Ellbogen

Here schonen means something like:

• to rest
• to take it easy on
• to avoid straining
• to go easy on

With body parts, it usually means not using them too much so they can recover.

Examples:

• Ich soll mein Knie schonen. = I should rest my knee.
• Du musst deinen Rücken schonen. = You need to take it easy on your back.

So it does not mean only to spare in the abstract English sense. In medical or physical contexts, schonen is a very common verb.

Because German often uses the accusative of duration to express how long something lasts.

So:

• einen Tag
• zwei Tage
• eine Woche
• drei Monate

Examples:

• Ich bleibe zwei Tage.
• Er arbeitet eine Stunde.
• Sie soll den Arm drei Wochen schonen.

In your sentence, zwei Tage means for two days.

English usually needs for, but German often does not.

Yes. Ellbogen and Ellenbogen are both standard German words for elbow.

So these mean the same thing:

• den Ellbogen schonen
• den Ellenbogen schonen

You may see one or the other depending on the speaker, region, or writing style, but there is no important meaning difference here.