Это единственный вопрос, который у меня есть.

Это here means this is or it is. It is commonly used to identify or introduce something:

• Это вопрос. = This is a question.
• Это мой друг. = This is my friend.

Этот is different: it is a demonstrative adjective meaning this, and it must go directly with a noun:

• этот вопрос = this question

So:

• Это единственный вопрос... = This is the only question...
• Этот единственный вопрос... would mean this only question..., which is a different structure.

In the present tense, Russian usually omits the verb to be (есть) when one thing is identified as another.

So English:

• This is the only question.

becomes Russian:

• Это единственный вопрос.

A literal есть is normally not used here. Saying Это есть единственный вопрос would sound unnatural in standard modern Russian.

Both единственный and вопрос are in the nominative singular masculine.

• вопрос is masculine singular nominative
• единственный matches it in gender, number, and case

This is because единственный вопрос is the thing being identified after Это:

• Это единственный вопрос. = This is the only question.

So the adjective agrees with the noun in the normal way.

Единственный means only, sole, or one and only.

In this sentence, it means there is just one question.

Compare:

• единственный вопрос = the only question
• один вопрос = one question
• только один вопрос = only one question

A useful nuance:

• один focuses on the number one
• единственный often emphasizes uniqueness: the only one

So единственный вопрос is very natural for the only question.

Because который у меня есть is a relative clause: it describes вопрос.

Russian normally separates this kind of clause with a comma:

• вопрос, который у меня есть

This is like English:

• the question that I have
• the question which I have

Russian punctuation is stricter here than English. Even where English might omit that, Russian still keeps the relative pronoun and uses a comma.

Который means which, that, or the one that.

It links the noun вопрос with the clause that describes it:

• вопрос, который у меня есть
• literally: the question, which I have
• naturally: the question that I have

So the full sentence means:

• This is the only question that I have.

Because it refers back to вопрос, which is:

• masculine
• singular
• nominative in this clause

Relative pronouns in Russian agree with the noun they refer to in gender and number. Their case depends on their role inside the relative clause.

Here который is the thing that exists with me / is had by me, so it is the subject-like element of есть, and nominative makes sense.

If the noun were feminine, neuter, or plural, the form would change:

• книга, которая...
• письмо, которое...
• вопросы, которые...

Literally, у меня есть means something like at me there is.

This is the standard Russian way to express possession:

• У меня есть вопрос. = I have a question.

Breakdown:

• у = by / at
• меня = me in the genitive case
• есть = there is / exists

So который у меня есть literally means which exists with me, but naturally it means which I have.

Because after the preposition у, Russian uses the genitive case.

The pronoun я changes like this:

• nominative: я = I
• genitive: меня = of me / me

So:

• у меня = at me / with me
• natural English: I have

This is a very common pattern, so it is worth memorizing as a unit:

• у меня есть = I have
• у тебя есть = you have
• у него есть = he has
• etc.

That is a very common source of confusion.

Russian often omits to be in sentences like:

• Он студент. = He is a student.

But есть is still often used in existential or possessive constructions:

• У меня есть вопрос. = I have a question.
• На столе есть книга. = There is a book on the table.

So in this sentence:

• the main clause omits is: Это единственный вопрос
• the relative clause keeps есть because it means have / there is: который у меня есть

They are two different grammatical patterns.

Usually, no—not in this sentence.

You can say:

• У меня вопрос. = I have a question.

But inside a relative clause, который у меня would sound incomplete and unnatural.

So:

• вопрос, который у меня есть = correct
• вопрос, который у меня = not correct in standard Russian

That is why есть is needed here.

Because Russian normally expresses possession with у + genitive + есть, not with иметь.

So:

• У меня есть вопрос. = normal, everyday Russian

Whereas:

• Я имею вопрос. sounds unusual, formal, old-fashioned, or non-native in many contexts

The verb иметь does exist, but it is used much less often than English to have. In ordinary speech, у меня есть is the standard pattern.

Normally, no. Russian usually needs the relative word.

English can say:

• the only question that I have
• the only question I have

Russian strongly prefers:

• единственный вопрос, который у меня есть

You generally cannot just remove который and leave:

• единственный вопрос у меня есть for the same meaning

That would change the structure and sound wrong or at least not mean the same thing.

It is grammatical and understandable, but depending on context, Russians might often choose a simpler sentence.

For example:

• У меня только один вопрос. = I only have one question.
• Это мой единственный вопрос. = This is my only question.

The original sentence:

• Это единственный вопрос, который у меня есть.

is perfectly valid, but it sounds a bit more explicit because it fully spells out the only question that I have.

So it is not wrong at all—just slightly more formal or more carefully structured than some everyday alternatives.

Yes, Russian word order is fairly flexible, but not every version sounds equally natural.

The original order is clear and neutral:

• Это единственный вопрос, который у меня есть.

Some alternatives are possible, but they may shift emphasis. For example:

• Это мой единственный вопрос.
• У меня есть только один вопрос.

These are more idiomatic in many everyday contexts.

So while Russian allows flexibility, the original sentence is already a good standard version.