[{"item":"journal","instock":[{"warehouse":"A","ele":[2,4,5]},{"warehouse":"C","ele":[8,5,2]},{"warehouse":"F","ele":[3]},{"warehouse":"K","ele":[2,8,4]}]}]

db.collection.find({"item":"journal"},{instock:{$filter:{input:"$instock",cond:{$in:[5,"$$this.ele"]}}}})