To run profiler you have do some operations, you have to input some tensor into your model.
Change your code as following.
import torch
import torchvision.models as models

model = models.densenet121(pretrained=True)
x = torch.randn((1, 3, 224, 224), requires_grad=True)

with torch.autograd.profiler.profile(use_cuda=True) as prof:
    model(x)
print(prof) 

This is the sample of the output I got.