if last head dense in TFBlenderbotSmallForConditionalGeneration uses the kernel which weights shared with embeddings, how about the bias?

Checking the PyTorch implementation, it seems that the language modeling head doesn’t use a bias, as seen here.

how can i get all the variables of the model include trainable and untrainable variables?

In PyTorch, you can get all parameters of a model as follows:
for name, param in model.named_parameters():
     print(name, param.shape)

cc’ing @Rocketknight1 for how to do this in Tensorflow.