La otoscopia muestra el conducto auditivo.

They are two different words:

• la otoscopia = the otoscopy, the examination or procedure
• el otoscopio = the otoscope, the instrument

In your sentence, the subject is the procedure/examination, not the tool, so la otoscopia is the correct choice.

Yes. Otoscopia is a feminine noun, so it takes la in the singular:

• la otoscopia
• una otoscopia

Many Spanish nouns ending in -ia are feminine, and otoscopia follows that pattern.

Muestra is the third person singular present indicative of mostrar (to show).

So here it means:

• la otoscopia muestra = the otoscopy shows

It is singular because the subject, la otoscopia, is singular.

A quick mini-pattern:

• yo muestro
• tú muestras
• él / ella / usted muestra
• nosotros mostramos
• vosotros mostráis
• ellos / ellas / ustedes muestran

In Spanish, the definite article is often used where English might also use the, especially with specific anatomical structures or when naming something clearly identifiable.

So:

• el conducto auditivo = the auditory canal / ear canal

Leaving out the article here would usually sound incomplete in a normal sentence.

Because in Spanish, adjectives usually come after the noun.

So:

• conducto = canal/duct
• auditivo = auditory

Together:

• conducto auditivo = auditory canal

This is the normal word order in Spanish medical and anatomical terms.

Yes, often you can. Both are used, especially in medical or anatomical contexts.

• conducto auditivo
• canal auditivo

Depending on the context, both can refer to the ear canal. Conducto auditivo may sound a bit more technical or anatomical, but canal auditivo is also very common and natural.

Yes. Spanish often uses the present tense in descriptions, reports, textbooks, and medical explanations.

So La otoscopia muestra el conducto auditivo sounds like a general descriptive statement, similar to English medical style:

• The otoscopy shows the auditory canal

This use of the present tense is very normal in formal and technical language.

Normally, no in this context.

• mostrar = to show, reveal, display
• enseñar = to teach, or to show someone something

In medical descriptions, mostrar is much more natural.
So:

• La otoscopia muestra... = correct and natural
• La otoscopia enseña... = not the usual medical phrasing

Yes. Auditivo means auditory and relates to hearing.

It belongs to a more formal or technical vocabulary set:

• oír = to hear
• audición = hearing
• auditivo = auditory

So conducto auditivo is the standard anatomical term.

A helpful approximation is:

• otoscopia: oh-toh-SKOH-pyah
• muestra: MWEHS-trah
• conducto auditivo: kohn-DOOK-toh ow-dee-TEE-boh

A few useful pronunciation notes for Spain:

• c before o sounds like k: co in otoscopia
• mu in muestra starts with a glide, roughly mwe
• v in auditivo is pronounced very similarly to b in Spanish
• In much of Spain, ti before a vowel can sound a bit like tyi, so auditivo may sound close to ow-dee-TYI-bo

This is the standard, neutral order:

• La otoscopia = subject
• muestra = verb
• el conducto auditivo = direct object

So the sentence follows the usual Spanish pattern:

Subject + Verb + Object

You can change word order in Spanish for emphasis, but this version is the most natural and straightforward, especially in formal or medical writing.