Each layer has its own default value for initializing the weights. For most of the layers, such as Dense, convolution and RNN layers, the default kernel initializer is 'glorot_uniform' and the default bias intializer is 'zeros' (you can find this by going to the related section for each layer in the documentation; for example here is the Dense layer doc). You can find the definition of glorot_uniform initializer here in the Keras documentation.
As for accessing the weights of each layer, it has already been answered here.