how to query nested json objects in mongodb?
I found the answer myself:

db.getCollection('mobiledashboards')
    .find
    (
        {
            "_id": ObjectId("58c7da2adaa8d031ea699fff") 
        },
        { 
            viewData: { $elemMatch : { "widgetData.widget.title" : "England" } }
        }
    )