I think, in "What does it look like?" "What" is the object, the subject is "it." "How does it look like" has no object, so it's not a complete sentence because

I think, in "What does it look like?" "What" is the object, the subject is "it." "How does it look like" has no object, so it's not a complete sentence because "look like" is a transitive verb (it requires a direct object when used in this context.)