Obviously no-one can tell you where the appropriate plugs and sockets are without knowing which motherboard and which case you have. I'm just baffled that you know that you need this connector without having looked, or at least reading the motherboard and case manuals, which would give you this information.
Anyway, the m/b manual will tell you where your USB header is, and I would imagine there is only one cable in the case with the appropriate plug on it. Trace the cable back to the USB sockets to be sure.