इसकी वजह क्या है?

इसकी is a possessive form built from यह (this, it, sometimes he/she in context). Here it means something like of this or its.

So in this sentence, इसकी points to some situation, event, or thing already being talked about:
इसकी वजह = the reason for this / its reason.

Because वजह is a feminine noun.

In Hindi, possessive forms like का / की / के agree with the noun that follows, not with the owner. Since वजह is feminine singular, you use की:

• इसकी वजह = its reason
• if the following noun were masculine singular, you would use इसका
• if plural or certain masculine forms, you would use इसके

वजह means reason, cause, or basis.

It is a very common everyday word. A near-synonym is कारण, which also means reason/cause, but कारण can sound a bit more formal or bookish.

So:

• वजह = common, natural, everyday
• कारण = also common, but often a little more formal

Hindi word order is often different from English. Literally, this sentence is close to:

Its reason what is?

That sounds strange in English, but it is normal in Hindi. The structure is:

• इसकी वजह = the reason for this
• क्या = what
• है = is

So Hindi puts the topic first, then the question word, and the verb है at the end.

Yes. इसकी क्या वजह है? is also natural and means the same thing.

Both are common:

• इसकी वजह क्या है?
• इसकी क्या वजह है?

The difference is very slight. In everyday use, either one is fine.

In standard Hindi, yes. है is the present-tense form of to be, and it completes the question.

So the full standard sentence is:

इसकी वजह क्या है?

In very informal speech, poetry, headlines, or dramatic style, Hindi sometimes drops forms of to be, but learners should keep है here.

This is a very common point of confusion.

• वजह = reason
• वजह से = because of, due to

So:

• इसकी वजह क्या है? = What is the reason for this?
• इसकी वजह से... = Because of this...

Examples:

• इसकी वजह क्या है? = What is the reason for this?
• इसकी वजह से समस्या हुई। = Because of this, a problem happened.

Not exactly.

• यह क्यों है? = Why is this? / Why is this the case?
• इसकी वजह क्या है? = What is the reason for this?

The second one feels a bit more explicit because it uses the noun वजह (reason/cause). It can sound slightly more analytical or explanatory.

So both ask about why, but they are phrased differently.

A simple learner-friendly pronunciation is:

is-kee va-jah kyaa hai

A few notes:

• इसकी = is-kee
• वजह = va-jah
  The व sound is somewhere between English v and w for many speakers.
• क्या = kyaa
• है = often sounds like hai or a bit like heh depending on accent and speed

A rough full pronunciation is:

is-kee va-jah kyaa hai

Yes. इसकी can mean his, her, its, or this one's, depending on context.

Hindi often relies on context more than English does. So इसकी वजह क्या है? could refer to:

• a situation
• an event
• an object
• a person
• a problem just mentioned

You understand the reference from the conversation.

Yes. A common more formal version is:

इसका कारण क्या है?

Here कारण is used instead of वजह. It means the same thing, but sounds a bit more formal.

You might compare them like this:

• इसकी वजह क्या है? = natural, everyday
• इसका कारण क्या है? = a bit more formal

Hindi often expresses this idea as its reason or the reason of this, where English prefers the reason for this.

So Hindi says:

• इसकी वजह = literally something like this's reason / its reason

English and Hindi organize this relationship differently, but the meaning is the same. This is a normal Hindi pattern, not something unusual about this sentence.