From within a view controller in a container view, how do you access the view controller containing the container?

You can use the prepareForSeguemethod in Vc1 as an embed segue occurs when the ContainerViewController is made a child. you can pass self as an obj or store a reference to the child for later use.

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    NSString * segueName = segue.identifier;
    if ([segueName isEqualToString: @"embedseg"]) {
        UINavigationController * navViewController = (UINavigationController *) [segue destinationViewController];
        Vc2 *detail=[navViewController viewControllers][0];
        Vc2.parentController=self;
    }
}

Edit: minor code fix