Is it paradoxical to ask what existence is without already knowing the meaning of the term "is"? A statement such as "there is a crate of oranges in front of me" seems like a statement about the "existence of oranges." But at the same time what does it mean to say that the "crate of oranges" exists? Existence seems like the most intuitive and indubitable metaphysical pronouncement and yet at the same time it evades clear definition. I suppose you can say "the orange crate exists because you can pick an orange up or it exists because you can observe it." But it seem like their is something more to saying something exists than that, but I can't put my finger on it.
I see your point - asking, "What is existence?" does seem to be like asking about the existence of existence. That is, the question seems to presuppose the very "thing" that is being inquired about. Existence surely does seem to evade clear definition. Maybe we define things in terms of attributes and to exist is to be a kind of place holder for predicates. Got me. Thanks for a great question