La boa è vicino a questa ancora.

In Italian, singular countable nouns normally need a determiner, such as an article or a demonstrative.

So:

• la boa = the buoy
• questa ancora = this anchor

Unlike English, Italian usually does not leave out the article in a normal sentence like this.

The accent distinguishes è = is from e = and.

So in this sentence:

• è is the 3rd person singular of essere: is
• e without an accent would mean and

This is a very common spelling point in Italian.

Vicino normally takes a before the thing or person that is being referred to.

So:

• vicino a questa ancora = near this anchor
• vicino a me = near me
• vicino al porto = near the harbor

English says near something without a preposition, but Italian usually uses vicino a.

This is a very natural question.

Vicino can behave a bit like a fixed expression in location phrases, especially in everyday use, so you may see it left as vicino.

However, you will also very commonly see agreement:

• La boa è vicina a quest'ancora.

That version is also very natural, and many learners are first taught it that way because vicina clearly agrees with la boa.

So the short answer is:

• vicino here can be understood as part of the expression vicino a
• vicina is also common and often feels more clearly grammatical to learners

Before a vowel, feminine singular questa is often shortened to quest'.

So many speakers would prefer:

• quest'ancora

That means:

• questa ancora is understandable
• quest'ancora is usually more natural before a vowel

This is similar to other forms such as:

• quest'acqua
• quest'isola

Because of its role in the sentence.

Here, ancora is preceded by questa, so it is clearly a noun:

• questa ancora = this anchor

The word ancora meaning again/still is an adverb, so it would be used differently:

• ancora qui = still here
• ancora una volta = again

In speech, the stress also helps:

• àncora = anchor
• ancóra = again/still

In normal writing, that stress is usually not marked, so context does the work.

Yes, it is understandable and basically natural.

That said, many native speakers would be a little more likely to say:

• La boa è vicina a quest'ancora. or
• La boa è vicino a quest'ancora.

The two changes you may hear most often are:

• quest'ancora instead of questa ancora
• sometimes vicina instead of vicino

So the given sentence works, but it is not the only natural way to say it.

Yes. The given order is straightforward and neutral:

• La boa è vicino a questa ancora.

But Italian can change word order for emphasis or style. For example:

• Vicino a quest'ancora c'è la boa. = Near this anchor there is the buoy.

That version shifts the focus toward the location first.

So the original sentence is the most direct structure, but not the only possible one.