kono setumei ni gimon ga aru.

The sentence uses the pattern:

X に 疑問がある

This literally works like:

• X に = about / regarding X
• 疑問がある = there is doubt / there are questions

So the structure is not I question X in the English-style verb sense. Instead, Japanese expresses it more like:

• There is doubt concerning this explanation
• I have doubts about this explanation

A lot of Japanese is built this way: instead of using a personal subject like I, it often describes a situation or state.

Here, に marks the target of the doubt.

So:

• この説明に = about this explanation / toward this explanation

In English, we often use about or with:

• I have doubts about this explanation
• I have a question about this explanation

In Japanese, に often marks the thing that an emotion, reaction, judgment, or mental attitude is directed toward.

So 説明に疑問がある means the doubt is directed at or toward the explanation.

Because ある does not take a direct object marked by を.

ある means to exist or to be present.
So 疑問がある literally means:

• a doubt exists
• there is a question/doubt

That is why 疑問 is marked by が, not を.

Compare:

• 時間がある = there is time / I have time
• 問題がある = there is a problem
• 疑問がある = there is a doubt / I have doubts

This is a very common Japanese way to express possession or internal states.

Because 疑問 is not a living thing.

In Japanese:

• ある is used for inanimate things, abstract things, and existence of non-living things
• いる is used for people and animals

Since 疑問 is an abstract noun, Japanese uses ある.

Examples:

• 本がある = there is a book
• 問題がある = there is a problem
• 猫がいる = there is a cat
• 先生がいる = there is a teacher

So 疑問がある follows the normal rule.

It can be translated as either question or doubt, depending on context, but the nuance is often closer to:

• doubt
• something that seems questionable
• a point you are not convinced about

So この説明に疑問がある often sounds stronger than just I have a question about this explanation. It can suggest:

• I am not fully convinced by this explanation
• There is something questionable about this explanation
• I have doubts about this explanation

If someone simply wants to ask for clarification, 質問がある is often more neutral:

• この説明について質問がある = I have a question about this explanation

So:

• 質問 = a question you want to ask
• 疑問 = doubt, uncertainty, something you find questionable

Because この directly modifies a noun.

• この = this + noun
• これ = this thing

So:

• この説明 = this explanation
• これ = this

You cannot say これ説明.
If you want to use これ, you would need a different structure, such as:

• これについて疑問がある = I have doubts about this

So in the original sentence, この is correct because it is attached to 説明.

Yes, the subject is omitted.

Japanese often leaves out subjects when they are obvious from context. So この説明に疑問がある could mean:

• I have doubts about this explanation
• He has doubts about this explanation
• We have doubts about this explanation

depending on the situation.

In many real conversations, the listener understands the subject from context, so Japanese does not need to state it.

If you want to make it explicit, you could say:

• 私はこの説明に疑問がある。 = I have doubts about this explanation.

But in natural Japanese, the 私は is often unnecessary.

が marks 疑問 as the thing that exists.

So:

• 疑問がある = there is a doubt / doubts exist

If you used は, the nuance would change. は introduces a topic or contrast.

For example:

• この説明には疑問がある。

This is also natural, but it adds a slight contrastive feeling, like:

• As for this explanation, there are doubts
• This explanation, at least, has some problems/questions

Notice that here には is a combination of に + は.

So:

• この説明に疑問がある = plain statement
• この説明には疑問がある = more contrastive/emphatic

Yes, it is natural, but it sounds somewhat formal or analytical.

It is the kind of sentence you might see in:

• discussions
• meetings
• essays
• formal criticism
• academic or business settings

In casual speech, people might say things like:

• この説明、ちょっとおかしくない？
• この説明、よくわからない。
• この説明には納得できない。

These can sound more conversational.

So the original sentence is definitely natural, but it has a slightly formal, thoughtful tone.

Yes, but the nuance usually leans more toward doubt than a simple information-seeking question.

If someone says:

• この説明に疑問がある

it often suggests:

• the explanation may be questionable
• the speaker is not fully satisfied
• the logic may not be convincing

If the speaker only wants more information, 質問がある is clearer and softer:

• この説明について質問がある = I have a question about this explanation

So while English might translate 疑問 as question sometimes, in this sentence doubt or reservation is often the better interpretation.

Yes, you can, but it is a different structure.

• この説明に疑問がある = I have doubts about this explanation
• この説明を疑問に思う = I find this explanation questionable / I doubt this explanation

The second version focuses more directly on the speaker’s mental judgment:

• 疑問に思う = to wonder about / to find questionable

So both are natural, but they feel slightly different:

• 疑問がある = states the existence of doubt
• 疑問に思う = emphasizes the act of feeling doubt

The original sentence is a little more neutral and matter-of-fact.