What dataiter.next() does is it gives you a B x 1 x H x W  image tensor and a B label tensor, where B is the batch size specified in your dataloader. If you want to see every training example, an easier way is to simply to a for loop on the trainloader directly.
for images, labels in trainloader:
    # training loop, reshape images if you have to
    print(image.shape)
    # torch.Size([1, 1, 28, 28])

Hope this helps!