“Levels” in Why-questions dont just occur in the sense of “chain of how many whys?” That is, one can ask a why to a why and a why to that why and so on, thus creating a chain and thus levels of why-questions. But there exist levels of another kind to a why-question – level of specificity of knowledge. These can be called “nested whys”, in a sense, also, like the earlier chain of whys preceding each other.
Consider this conversation between 2 people – A & B :
A: John gave a ball to Jack.
B: Why did he give a ball to Jack?
A: Because he wanted a favour from Jack.
B: I know that; what favour did he want from Jack? When I asked – Why did he give a ball to Jack, I meant that very thing – What favour did John want from Jack for giving a ball to him?
Now, it may also happen that A tells the favour and B says that he knew that also and actually wanted to know something specific about that favour itself…..(which is what he meant by asking ‘why did John give a ball to Jack?’ in the first place).
This can go on and on, creating nested levels of specificity of knowledge of the reason (which a ‘why’ seeks to know). This is another dimension of levels of a why-question.
A WHY-question is thus at a “level”, in at least 2 such above described senses – plain whys preceding each other, and the level of specificity of knowledge of reason.