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

Is the function exported? If not you may have to find the address your self, by searching for certain fragments or memory or using the exact address/offset of it (how ever this can fail if the file gets changed)