Get all the objects within the layer

Will tell you the items directly underneath the layers. If you want to keep going in groups that are inside the layers, keep adding to it.

doc = app.activeDocument;

layers = doc.layers;

for (var x = 0; x < layers.length; x++){

    for (var i = 0; i < layers.pageItems.length; i++){

        alert(layers.pageItems.name);

    }

}