If what you want is to define the type of a function that takes an Object as parameter and returns nothing, the syntax would be:
typedef void TNotifyEvent( Object Sender );
EDIT, as answer to the comment.
Yes, you can define the type of a function, and that type can later be used in different contexts with different meanings:
TNotifyEvent func; // function declaration (weird as it might look)
// same as: void func( Object Sender );
TNotifyEvent *fp = func; // function pointer declaration -- initialized with &func
void func( Object Sender ) // cannot use the type when defining the function
{}
void foo( TNotifyEvent f ); // compiler translates to TNotifyEvent * f
// just as 'int a[5]' is converted to 'int *a'
// in function parameter lists.