What kind of information about the alpha channel? If you do an alpha-to-selection the selection is a copy of the alpha channel of the layer, and you can save it to a channel. You can also create a layer mask and initialize it to the alpha-channel of the layer. In both case you obtain a drawable that is a copy of the layer's alpha channel. The first technique is a bot more suitable if you don't want to modify it, the second is better if you intend to apply back changes.
But I have the nagging feeling that this is a XY problem. What are you trying to achieve?
But I have the nagging feeling that this is a XY problem. What are you trying to achieve?