Can we use affirmative sentences word order in interrogative questions

Question

In case of interrogative questions, when we already have questioning words like When, Which, Where,... with subjects in 3nd person form (he, she, it) I tend to omit auxiliary word and use affirmative sentence word order. Which seems to be incorrect according to English grammar. I want to know is it totally wrong and prohibited to use this word order, or it could be used sometimes, and if so, when and why? Let's see some simple examples:

1. Affirmative: This bus goes to London.
2. Correct question with Wh* word: Where does this bus go?
3. Incorrect form which I tend to use: Where this bus goes?

Another example:

1. Affirmative: This dog likes you.
2. Correct: Who does this dog like?
3. Incorrect(?): Who this dog likes?

When and why "we can use" (or "can we use"?) the word order showed in examples above under number 3?

PS: "When can we use a wrong word order?" - feels to me like a double questioning. Seems unnatural to me. Am I wrong?

Answer 1

Your "Incorrect" examples are incorrect as question sentences. They are just wrong, in the same way that "Like dogs I" is "wrong".

Your "correct" examples are correct as question sentences.

The phrase "who this dog likes" is not a sentence, but it may appear as a noun phrase or as a relative clause: "The man who this dog likes is sitting over there."

With "can"

We can play piano. (Affirmative)

What can we play? (question)

What we can play (incorrect, though it could be a noun phrase in a larger sentence "Please tell us what we can play".

But note, when the question is about the subject, the word order is:

We can play piano. (Affirmative)

Who can play piano? (question)

Who can piano play? (incorrect, unless pianos can play people.)