[{"name":"John Doe","atributes":{"alive":{"start":15816412115,"end":1516186131},"job":"developer","title":"senior",}},{"name":"John Cena","atributes-2017":{"alive":{"start":15816412115,"end":1516186131},"job":"dancer",}}]

db.collection.aggregate([{$group:{_id:null,docs:{$push:"$$ROOT"}}},{$project:{docs:{$map:{input:"$docs",as:"d",in:{$objectToArray:"$$d"}}}}},{$unwind:"$docs"},{$match:{"docs.v.title":{$exists:true}}},{$replaceRoot:{newRoot:{$arrayToObject:"$docs"}}}])