Edit in JSFiddle

var A = _.extend({name:'A'}, Backbone.Events);
var B = _.extend({name:'B'}, Backbone.Events);
var C = _.extend({name:'C'}, Backbone.Events);

var whosListeningToMe = function(){console.log(this.name);};

B.listenTo(A, 'whosListeningToMe', whosListeningToMe);
B.listenTo(C, 'whosListeningToMe', whosListeningToMe);

A.trigger('whosListeningToMe'); //logs B
C.trigger('whosListeningToMe'); //logs B

B.stopListening(A);

//B stop listening to A so nothing is logged but, B is still listening to C
A.trigger('whosListeningToMe');
C.trigger('whosListeningToMe'); //logs B