La nova dungito montris grandan kapablon dum la laborintervjuo.

A useful breakdown is:

• La nova dungito = the subject, the new employee
• montris = the verb, showed
• grandan kapablon = the direct object, great ability
• dum la laborintervjuo = a time phrase, during the job interview

So the structure is basically:

subject + verb + object + time expression

Esperanto has no indefinite article. There is a word for the: la, but there is no separate word for a/an.

So:

• la nova dungito = the new employee
• grandan kapablon = great ability or a great ability, depending on context

This is very normal in Esperanto.

The -n marks the direct object.

Here, the thing being shown is grandan kapablon, so kapablon gets -n.

Because grandan describes kapablon, the adjective must agree with the noun. In Esperanto, adjectives match nouns in:

• number: singular/plural
• case: whether they take -n

So:

• granda kapablo = great ability
• grandan kapablon = great ability as a direct object

This agreement is one of the most important patterns in Esperanto.

Because la nova dungito is the subject, not the direct object.

In this sentence:

• la nova dungito does the action
• grandan kapablon receives the action

Only the direct object takes -n here, so:

• nova dungito = subject
• grandan kapablon = object

If dungito were the direct object in another sentence, then you would use dungiton, and the adjective would also change: novan dungiton.

The ending -is marks the past tense in Esperanto.

So:

• montras = shows / is showing
• montris = showed
• montros = will show

This is one of the nicest features of Esperanto: verb endings are very regular.

Here dum means during.

It introduces a time expression:

• dum la laborintervjuo = during the job interview

A useful detail: dum can also mean while when it introduces a whole clause.

For example:

• dum la intervjuo = during the interview
• dum li parolis = while he was speaking

In your sentence, it is followed by a noun phrase, so it means during.

Because after a preposition like dum, nouns normally do not take the accusative -n.

So:

• dum la laborintervjuo = correct

In Esperanto, the accusative after prepositions is mainly used to show direction in some cases, not ordinary location or time.

Here there is no idea of motion toward something, so laborintervjuo stays without -n.

Esperanto commonly forms compound words by joining roots together.

Here:

• laboro = work
• intervjuo = interview

So laborintervjuo literally means something like work-interview, that is, job interview.

In Esperanto compounds, the main idea usually comes last. So this is a kind of intervjuo related to laboro.

This kind of compounding is very common and very natural in Esperanto.

Dungito comes from the root dung-, which is related to hiring/employing.

You can think of it like this:

• dungi = to hire / employ
• -it- = someone who has been affected by the action
• -o = noun ending

So dungito is literally a hired person, which gives the meaning employee.

This is a great example of how Esperanto builds words in a very logical way.

Because la goes before the whole noun phrase, not before every word.

So:

• la nova dungito = the new employee

You do not say la nova la dungito.

Also, la never changes form. It stays la no matter what comes after it:

• la dungito
• la nova dungito
• la novaj dungitoj
• la novan dungiton

That makes articles much simpler than in many languages.

Yes, to some extent.

Because Esperanto marks the direct object with -n, the sentence can be rearranged more freely than English without losing the basic meaning.

For example, these are still understandable:

• La nova dungito montris grandan kapablon dum la laborintervjuo.
• Dum la laborintervjuo la nova dungito montris grandan kapablon.
• Gravan kapablon la nova dungito montris dum la laborintervjuo.
  (though this changes the emphasis)

The most neutral order is still the original one, but Esperanto allows flexibility because the grammar marks the roles clearly.