A juzgar por la prueba práctica, demuestra competencia profesional.

A juzgar por means judging by, to judge from, or based on.

In this sentence, A juzgar por la prueba práctica means judging by the practical test.

It is a fixed expression in Spanish and is very common in both spoken and written language. It is often used to introduce the basis for a conclusion:

• A juzgar por su acento, es de Sevilla.
• A juzgar por los resultados, el plan funciona.

So in your sentence, the speaker is saying that the conclusion comes from the practical test.

Spanish normally uses the fixed phrase a + infinitive + por here: a juzgar por.

Even though English often uses an -ing form (judging by), Spanish does not usually say juzgando por in this meaning. The standard expression is:

• A juzgar por...

So this is something best learned as a chunk rather than translated word for word from English.

Here por means something like by, from, or on the basis of.

It introduces the evidence or source used to make a judgment:

• A juzgar por su cara... = Judging by his/her face...
• A juzgar por los datos... = Judging from the data...

So por la prueba práctica tells you what the judgment is based on: the practical test.

The subject is not explicitly stated because Spanish often leaves subject pronouns out when the verb form already makes the grammar clear.

Demuestra is the third-person singular form of demostrar, so it can mean:

• he demonstrates
• she demonstrates
• it demonstrates
• you demonstrate (formal singular, usted)

Without more context, you cannot know exactly who the subject is. Spanish often relies on context for this.

For example, if the previous sentence mentioned la candidata, then demuestra would naturally mean she demonstrates.

The present tense here expresses a current judgment or evaluation.

Demuestra competencia profesional means something like:

• shows professional competence
• demonstrates professional competence

This is very natural in reports, assessments, and formal comments. Spanish often uses the present tense to state conclusions in a direct, factual way.

If you changed the tense, the meaning would shift:

• demostró = demonstrated / showed in the past
• demostrará = will demonstrate

So the present tense fits a general or current assessment.

Prueba práctica means practical test, practical exam, or hands-on assessment.

• prueba = test, trial, assessment
• práctica = practical, hands-on

It refers to a test based on doing something in practice, not just answering theoretical questions.

In Spain, this kind of phrase is common in educational, professional, and official evaluation contexts.

In Spanish, most descriptive adjectives normally come after the noun.

So:

• prueba práctica = practical test
• competencia profesional = professional competence

This is the usual word order in Spanish. English often puts adjectives before the noun, but Spanish usually places them after it.

Spanish often omits the article when talking about a quality, category, or abstract concept in a general sense.

So demuestra competencia profesional means shows professional competence in a broad, general way.

If you said demuestra una competencia profesional, it would sound less natural in many contexts, because it suggests a certain professional competence as one instance or type. The version without the article is more natural for evaluations and formal statements.

Compare:

• Tiene experiencia. = He/She has experience.
• Muestra interés. = He/She shows interest.
• Demuestra competencia profesional. = He/She demonstrates professional competence.

No. Here competencia means competence, ability, or professional capability, not competition.

This is a very important false friend for English speakers.

In Spanish, competencia can mean different things depending on context:

• competence / ability
• authority / jurisdiction
• competition / rivalry in some contexts

In competencia profesional, it clearly means professional competence: the ability to do a job properly and effectively.

Yes, but the nuance is slightly different.

• A juzgar por la prueba práctica = judging by the practical test
  This emphasizes that the speaker is drawing a conclusion from the evidence.

• Según la prueba práctica = according to the practical test
  This sounds more like the test itself is the source of the information.

Both can work, but a juzgar por is especially natural when you want to present a conclusion based on what you have observed.

Yes, it sounds fairly formal and evaluative.

It would fit well in contexts like:

• assessment reports
• training evaluations
• official comments
• professional or academic feedback

The combination of A juzgar por... and demuestra competencia profesional gives the sentence a formal, objective tone. In casual conversation, a speaker might say something simpler, depending on the situation.