I used a function to analyse it manually. I'm not sure if there're better approaches. Here's my code for a dlnetwork object myDLnet (thus the code works for 2019b but not sure for the older version):
num_para=find_num_para(myDLnet)
function num_para=find_num_para(myDLnet)
layers=myDLnet.Learnables.Value;
num_layers = size(layers,1);
num_para=0;
for i=1:num_layers
num_para=num_para+prod(size(layers{i}));
end
end
