You are asking me pick something in a class that by definition is completely outside of my realm of all knowledge or concept of any type. By definition I cannot pick something in that class of items.
That is what I meant by:
(if you do, insert something else you don't know, how many teeth a Tyrannosaurus have etc.)
etc = something else you don't know.
Yes you can't pic it. But for there purposes you just have to entertain the thought. Can you conceive of a thing you don't know?
It exactly means that. You can't know whether or not you know something unless you've thought about it. Babies can't do that and they lack a belief in god(s), therefore they are atheists. Try again.
When I ask you about it, you will know if you know about it, without thinking about it.