Database
[{"_id":ObjectId("5d9df11b0e0a6e032bf3117f"),"body":"","comments":[{"comment":"","_id":ObjectId("5d9df46e0e0a6e032bf31182"),"replies":[{"reply":"reply to comment ","_id":ObjectId("5d9bec26301798056bb07ab5")},{"reply":"reply to comment 3 ","_id":ObjectId("5d9bec26305798056bb07ab5")},]},],}]
Query
db.collection.find({"comments.replies._id":ObjectId("5d9bec26301798056bb07ab5")},{"comments.replies.$":1})