How many neurons a deep learning model (specifically a CNN) does have?
I hope you are talking about the parameter count in a convolutional neural network.
Below is basic understanding about calculating the parameters. After getting this, it would be self explanatory.
kernel count = k
kernel size = (a, a)
depth of input = d 
Total number of parameters: k*(a*a)*d + k

Now, for below scenario which has one input layer with one con2d layer.

To cross check the number of parameters, we need k,d,a:
 k = 64, d = 3, a*a = 3*3

Total parameters: 64*(3*3)*3 + 64 = 1792

Hope its clear now.