tonari no inu ha yoru ni yoku hoeru node, nemurenaikoto ga arimasu.

It can mean either, depending on context.

• 隣 = next door / neighboring
• の links 隣 to 犬
• 犬 = dog

So 隣の犬 is literally the neighboring dog. In natural English, that often becomes either:

• the neighbor's dog
• the dog next door

Here, の is not only possession. It can also mean the X that belongs to / is connected with / is next to Y.

は marks the topic of the sentence: as for the dog next door...

So the sentence is setting up 隣の犬 as the thing being talked about, and then saying something about it:

• 隣の犬は = as for the dog next door,
• 夜によく吠える = it often barks at night

If you used が instead, it would sound more like you are identifying or emphasizing the dog next door as the one that barks. That can be correct in some contexts, but は is more natural here for a general statement or complaint.

に marks a point or time when something happens.

• 夜 = night
• 夜に = at night

So 夜によく吠える means often barks at night.

With time words, に is sometimes omitted, and with words like 夜, both styles can appear. But 夜に is very natural and clearly marks the time. It sounds slightly more explicit.

Good question. よく can mean different things depending on context.

Here it means often or frequently, not well.

So:

• よく吠える = often barks

Compare:

• 日本語をよく話す can mean speaks Japanese well
• よく行く usually means go often

In this sentence, because it is about barking at night, often is the natural meaning.

Because ので connects clauses, and the clause before it normally uses the plain form.

So:

• 吠えるので = because it barks / since it barks

This is normal grammar.

If the whole sentence were made polite, you could also see:

• 吠えますので

That sounds more formal or polite. But in ordinary neutral written Japanese, plain form + ので is very common.

Both can mean because, but the nuance is a little different.

• ので sounds softer, more explanatory, and a bit more objective
• から sounds more direct and more personally assertive

So:

• 吠えるので、眠れないことがあります。 = Because it often barks, there are times when I can't sleep.
• 吠えるから、眠れない。 = Because it barks, I can't sleep.

In this sentence, ので fits a calm explanation of the reason.

Japanese often leaves out the subject when it is understood from context.

Here, the person who can’t sleep is most naturally:

• the speaker
• or possibly the speaker's household, depending on context

So even though I is not stated, the sentence naturally implies I sometimes can't sleep.

This is very common in Japanese. If the speaker wanted to be more explicit, they could say:

• 私は眠れないことがあります。

But that is often unnecessary.

眠れない means cannot sleep or am unable to sleep.

It is different from 眠らない, which means do not sleep or won’t sleep.

So:

• 眠らない = not sleeping by choice / not sleeping as a fact
• 眠れない = unable to sleep

That is why 眠れない is the natural choice here. The barking dog is making sleep impossible, not causing a voluntary decision not to sleep.

Because 眠れないことがあります means there are times when I can’t sleep or I sometimes can’t sleep.

It does not mean the speaker can never sleep. It only says this happens sometimes.

Compare:

• 眠れない。 = I can’t sleep.
• 眠れないことがあります。 = There are times when I can’t sleep / I sometimes can’t sleep.

So the full sentence has a softer, more limited meaning: the dog often barks at night, and as a result, the speaker is sometimes unable to sleep.

こと turns the whole clause before it into a noun-like idea.

So:

• 眠れない = can’t sleep
• 眠れないこと = the fact/event of not being able to sleep

Then あります means exists / there is.

So the whole pattern literally works like:

• 眠れないことがあります
• There are occasions of not being able to sleep
• natural English: There are times when I can’t sleep

This verb/adjective + ことがある pattern is very common for saying sometimes or there are occasions when...

Because あります is an existence verb: there is / there are.

In this pattern, こと is treated as the thing that exists, so it takes が:

• 眠れないことがある = there are times when I can’t sleep

So:

• が marks the event as the subject of ある
• を would be wrong here, because ある does not take a direct object in this pattern

You may sometimes see ことはある, but that is a different structure with contrast or emphasis, such as it does happen, at least sometimes. That is not the neutral meaning here.