get the number of pixels in the alpha channel of an image layer whose transparency value is 0.

Duplicate post:

https://community.adobe.com/t5/photoshop-ecosystem-discussions/scripting-get-the-number-of-pixels-in-the-alpha-channel-of-an-image-layer/m-p/12857887

In Photoshop terminology a Layer can have Transparency, a Layer Mask, a Vector Mask, but »alpha channel« does not apply. 

Could you please post screenshots with the pertinent Panels (Toolbar, Layers, Channels, Options Bar, …) visible to clarify what you mean?