We cannot say:

• What your name is?

Let's see why. Maybe if we don't hear what somebody said, we can use an echo question:

• Your name is what?

Another name for this type of question is an in situ question. We use the word what to show which word we didn't hear, or which word we don't know. But we leave the word what in the same place as the word we want to know.

This is a question, but it uses the same word order as a normal sentence:

• Your name is Bob.

We usually don't make questions like this. We usually move the wh- word to the front of the sentence when we make a question:

• What blah blah blah blah?
• Who blah blah blah blah?
• Where blah blah blah blah?

If the wh- word needs to move to the front of the question, then we also need to change the order of some other words. We change the subject and the auxiliary verb. Let's look at the in situ question again to see what the subject and the auxiliary verb are:

• Your name is XXXX?

The auxiliary verb here is is. The verb BE is always an auxiliary verb, even when it is the only verb. In normal, canonical, sentences the subject is the noun phrase before the auxiliary. Here the subject is your name.

If we want to make this question with what at the beginning of the question, then we need to invert, to change round, the subject and the auxiliary like this:

• What [is] [your name]?
• What is your name?

If we do not invert the subject and the auxiliary, the sentence is ungrammatical:

• *What your name is? (wrong).

Hope this is helpful!

We cannot say:

• What your name is?

Let's see why. Maybe if we don't hear what somebody said, we can use an echo question:

• Your name is what?

Another name for this type of question is an in situ question. We use the word what to show which word we didn't hear, or which word we don't know. This is a question, but it uses the same word order as a normal sentence:

• Your name is Bob.

We usually don't make questions like this. We usually move the wh- word to the front of the sentence when we make a question:

• What blah blah blah blah?
• Who blah blah blah blah?
• Where blah blah blah blah?

If the wh- word needs to move to the front of the question, then we also need to change the order of some other words. We change the subject and the auxiliary verb. Let's look at the in situ question again to see what the subject and the auxiliary verb are:

• Your name is XXXX?

The auxiliary verb here is is. The verb BE is always an auxiliary verb, even when it is the only verb. In normal, canonical, sentences the subject is the noun phrase before the auxiliary. Here the subject is your name.

If we want to make the question with what at the beginning of the question, then we need to invert, to change round, the subject and the auxiliary like this:

• What [is] [your name]?
• What is your name?

If we do not invert the subject and the auxiliary, the sentence is ungrammatical:

• *What your name is? (wrong).

Note that the order of the phrases in the sentence is:

• What (complement), is (verb), your name (subject)

Hope this is helpful!