Hola, I am not a teacher, but as a Spanish native speaker, I will try to answer you. Usually, the proper way to make a Spanish question is placing first the interrogative word (quién, cómo, cuándo), afterwards the verb (soy, es, come, etc.) and after all that the subject (el niño, tu pregunta, etc.)
Therefore, you need to place first the interrogative word (What), aftewards the verb (es) and at the end the subject (tu pregunta): "What is your question" = "¿Cuál es tu pregunta?".
"¿Cuál pregunta tu es?" does not make sense in Spanish because the order is different. Also "tu" (without accent mark) is used as a possessive adjective and it needs a grammatical noun to work properly. It cannot go with a verb afterwards, it has to be followed by a proper noun, like mi casa, tu pregunta, su perro, etc.
The second one is not correct. You should say: "¿Cuánto pan come el niño (how much bread does the child eat? or "Cuándo come pan el niño/When does the child eat bread"? If you see, you place the interrogative pronoun first (cuánto, cuándo, qué, cuál) and afterwards the verb (es, come, soy). and after all that, the subject (tu pregunta, el niño, tú, etc.).
"Who are you?" should be translated as: "¿Quién eres tú?", just following the same structure: Interrogative word first, verb second and last subject (just like in "¿Quién soy yo?").
I hope it helps and it does not confussed you more. Good luck! :)