This works for me:
class FashionMNISTmodel:  
    def __init__(self):    
        self.net = self.FashionNet(torch.relu)
        
    class FashionNet(nn.Module):
        def __init__(self, activationfcn):
            super().__init__()
    
    
model = FashionMNISTmodel()
print(model)
print(model.net)