C++ Help (Hooking a function)

Yea like that, but i already have hooked Check_Registration, and inside the sdk they can use like you said: Callback_NotifyOnline();

now i want to hook also Callback_NotifyOnline();, but looking thru the sdk, its not defined nowhere except in the routine its self here:

void Check_Registration (
int Registered,
int Licenses,
int LicenseType,
int ChkSum,
int RESERVEDA,
int ( *Callback_CheckDate )( DATE *pDATE ),
void ( *Callback_NotifyOnline)( DATE *pDate, int ChkSum )  // Only time its defined. ) 
{

}

Thanks for all the help