Find duplicate inside an array mongodb

You're not far off just some minor tweaks needed:

db.getCollection("users").aggregate(    [        {             "$unwind" : "$profile.organizations"        },         {             "$group" : {                "_id" : {                    "dup" : "$profile.organizations",                     "id" : "$_id"                },                 "count" : {                    "$sum" : 1.0                }            }        },         {             "$match" : {                "count" : {                    "$gt" : 1.0                }            }        },         {             "$group" : {                 _id: "$_id.id",                 Dupes: {$push: "$_id.dup"}            }        }    ], );

You can use below aggregation

db.collection.aggregate([  { "$project": {    "Dupes": {      "$filter": {        "input": { "$setUnion": ["$profile.Organizations"] },        "as": "s",        "cond": {          "$gt": [            { "$size": {              "$filter": {                "input": "$profile.Organizations",                "cond": { "$eq": ["$$this", "$$s"] }              }            }},            1          ]        }      }    }  }}])