Do you know Spar
>r™ ut 'mm mi or navmg oecome acquainted), mis is why
you use ft] o TI ^   for knowing people and being familiar with places
Do you know Mr. Kawamura's address?
No, I don't. But I'll know (lit, it will be clear) if I check it
Both t>fr U Sit A; and ft] U Si±A> can be used for / don't know, but the nuance is quite different. 3EP U SitA* can imply \ don't know and have no reason to, so it can sound a bit rude if the question is one that you could be expected to know the answer to. That is why, when you ask a store clerk a question about the merchandise, he or she answers with tofr U SiiTufa instead of ft] U Sit A/. (The fa makes it clear that the meaning is / don't know, not / don't understand you.)
In fact, saying ft] bftO directly to another person's face is a way of saying / disapprove of what you are doing and want nothing to do with you. Furthermore, since ft]-5 refers to finding out something that you didn't have any reason to know, it sounds odd to use ft] U Si±A> in reference to something concerning yourself, such as your own future plans or your own wants.
However, ft] U Sit Ay is a perfectly acceptable response when you don't know a person, are unfamiliar with a place or idea, or have no expertise in a certain subject area.