How to check if an anchored frame is empty or not?

You could use something like this:

#target framemaker
var doc = app.ActiveDoc;
var frames = getEmptyAnchoredFrames (doc);
deleteFrames (frames);
function getEmptyAnchoredFrames (doc) {
    var graphic, frames = [];
    graphic = doc.FirstGraphicInDoc;
    while (graphic.ObjectValid () === 1) {
        // Test for an anchored frame.
        if (graphic.constructor.name === "AFrame") {
            // See if the anchored frame is empty.
            if (graphic.FirstGraphicInFrame.ObjectValid () === 0) {
                frames.push (graphic);
            }
        }
        graphic = graphic.NextGraphicInDoc;
    }
    
    return frames;
}
function deleteFrames (frames) {
    for (var i = 0; i < frames.length; i += 1) {
        frames.Delete ();
    }
}