An example implemented with Spektral (for TF, unfortunately) could do graph signal classification. You may find the code here graph_signal_classification_mnist.py 2. One thing is that you may need to use self.flatten = Flatten() instead of using GlobalSumPool() of Spektral.
Even though I am keen to re-write the code by using PyTorch Geometric, I cannot find a dataloader similar to the one (i.e. mixedloader) used by Spektral in the case with only one graph and multiple graph signal instances.