To visualize the kernels, just get the weight parameter of the specific layer by addressing the attribute and try to plot it e.g. using matplotlib. E.g. if your model has 3 conv layers defined as self.conv1 = nn.Conv2d(...), you could get the kernels via:
model = MyModel()
kernel = model.conv2.weight.detach()
To get activations for a specific input, have a look at this post.