Which regularization in convolution layers (conv2D)
Nowadays, people don't tend to add much regularisation like $L_2$ to convolutional networks. Usually, regularisation is achieved through the use of techniques like dropout and batch normalisation (although exactly how this regularisation actually happens is not well understood). 

Having said that, it may be different for your particular problem. I recommend that after experimenting with dropout and batch norm, you should experiment with $L_2$ and see how the predictive performance is affected on a validation set.