Well, it depends on who you are asking. For people who have studied philosophy, it does not have to do with abstraction or hermeneutics, or with the answer. For example, I would identify the question “What is Descartes’ cogito, and what did he mean by it?” as philosophical, and this is a straightforward question with a factual answer and not a huge amount of space for varying interpretations.
This is much of what we do, actually – study past philosophers and try to get a handle on what they were doing, on how their work builds off of previous philosophers, and on what their ideas mean for what we currently think about things. Nothing mysterious, just the history of ideas. We do also build on their work, of course, but we generally don’t do it by posing questions to one another like “Why is the world the way it is?”, but rather pose questions like “Can we find out something new about Amery’s account of ressentiment by viewing it in light of Rorty’s notion of ironism?” or “Was Derrida saying what most people think he was saying, or was it something else?” or “In what ways can we suggest a melding of Irigaray & Kristeva’s ideas about femininity, and in what ways do they differ?”
The “big” ones, like about how we know what we know, why the world is as it is, whether God exists, how mind, body, and world relate to each other, – these are also philosophical questions, ones that do have the qualities you identify above. These are more like broad outlines of inquiry than anything else, though – they are, in fact, how we define different areas of study in philosophy. In order, the questions above describe Epistemology, Metaphysics, Philosophy of Religion, and Philosophy of Mind.
You know when a question is truly philosophical when you have a reasonable sense of what philosophy is and can identify it as such. It’s a matter of interpretation. Ultimately, I think one can interpret almost any question as philosophical, down to “How old are you?” and “What time is it?” – it depends on the context the interlocutor was asking the question in.