It is not a full sentence but it means: there is a _____ on the wall.
"Hay en la clase" means "There is in the class" in English.
"Hay un amigo en mi" translates to "There is a friend in me" in English.
"Que hay en tu escuela" in English means "What is in your school?"
"cuántos cuartos hay en la casa?" means "How many rooms are there in the house" in English.
The litteral translation is - There are students in the class Mexico
It means "What is there in the students desk?"
"How many days are there in a year?"
how many people are there in your family?
It means "What is there in the big cities?"
A good interpretation would be "What's in class?"
Que -> what en > inside tu > you or your casa>house hay> there is/are Que hay en tu casa means, "what is there in your house?"
cuantos dias hay en una semana