Hi @Aryan_Asadian,
Let’s assume that you have models.resnet50 from torchvision.
my_resnet = models.resnet50(pretrained=True)

If you want to register the hook on the first on the conv2 of the very first bottleneck block you will write:
my_resnet.layer1[0].conv2.register_forward_hook(hook_fn)

As you can see, modules are called by name/id and Sequential blocks element by index.
To find what are the names of the submodules you can print the model.
I hope that I understood correctly what you mean by muti-model net.