Kiam mi ne scias la respondon, mi silentas.

Kiam is the normal word for when in a time clause.

So Kiam mi ne scias la respondon, mi silentas literally means When I do not know the answer, I stay silent / I am silent.

In natural English, this can sometimes overlap with if, because English often uses if for repeated situations: If I don’t know the answer, I keep quiet. But in Esperanto, kiam keeps the basic idea of when rather than if.

If you wanted a more purely conditional idea, you would normally use se: Se mi ne scias la respondon, mi silentas.

The ending -as marks the present tense in Esperanto.

• scii = to know
• scias = know / am knowing
• silenti = to be silent, keep silent
• silentas = am silent / keep silent

In this sentence, the present tense is being used for a general habit or repeated truth, just like in English:

• When I don’t know the answer, I stay quiet.

So -as does not only mean something happening right now at this exact second. It can also describe a usual pattern.

Because la respondon is the direct object of scias.

In Esperanto, direct objects usually take the -n ending:

• respondo = answer
• respondon = answer as a direct object

Here, mi scias la respondon means I know the answer. The thing known is the answer, so it gets -n.

Without -n, it would be grammatically wrong in standard Esperanto.

La is the definite article, meaning the.

So:

• respondo = an answer / answer
• la respondo = the answer

In this sentence, the speaker means a specific answer: the answer to whatever question or situation is being discussed. That is why la is natural here.

Esperanto has only one article, la, and it does not change for gender, number, or case. Even when the noun gets -n, the article stays the same:

• la respondo
• la respondon

In Esperanto, ne usually goes directly before the word or part being negated.

So:

• mi scias = I know
• mi ne scias = I do not know

That placement is very regular and easy to remember. If you want to negate the verb, put ne before the verb.

It can mean both, depending on context.

The verb silenti means to be silent or to keep silent. In this sentence, natural English would often use:

• I stay silent
• I keep quiet
• I say nothing

So mi silentas is not just a description of your personality. Here it describes what you do in that situation.

Yes. Esperanto word order is fairly flexible, especially with clauses like this.

You can say:

• Kiam mi ne scias la respondon, mi silentas.
• Mi silentas, kiam mi ne scias la respondon.

Both are correct. The first version puts the when-clause first, which feels very natural. The second starts with the main clause first.

Because respondon has the -n ending, its role stays clear even if word order changes.

The comma separates the subordinate clause from the main clause.

• Kiam mi ne scias la respondon = subordinate clause
• mi silentas = main clause

Using a comma here is normal and helps readability. Esperanto punctuation is generally similar to what English speakers expect in this kind of sentence.

Yes. This is a very common Esperanto pattern.

The root is respond-, and different endings make different parts of speech:

• respondi = to answer
• respondo = an answer
• responda = answering, responsive
• responde = in answer, responsively

This is one of the helpful things about Esperanto: once you know the root, you can often recognize a whole family of related words.

Normally, scii is the better choice here.

• scii = to know a fact, know information
• koni = to know a person, place, or thing through familiarity

So:

• Mi scias la respondon = I know the answer
• Mi konas lin = I know him

An English speaker often has to learn this distinction, because English uses know for both ideas.

Most naturally, it describes a general habit or repeated situation.

Kiam mi ne scias la respondon, mi silentas means something like:

• Whenever I don’t know the answer, I stay quiet.

The present tense -as often works this way in Esperanto, just as in English:

• When it rains, I stay home.
• Kiam pluvas, mi restas hejme.

So even though the verb is present tense, the meaning is broader than just one single moment.