Database
db={"FirstCollection":[{_id:"601d07fece769400012f1280",FieldName:"Employee",Type:"Chapter"}],"SecondCollection":[{_id:"601d11905617082d7049153a",SurveyId:"601d118e5617082d70491539",TemplateName:"",Elements:[{_id:"601d07fece769400012f1280",FieldName:"Employee",Type:"Chapter"},{_id:"601d07fece769400012f1281",FieldName:"Contract",Type:"Chapter"}]}]}
Query
db.FirstCollection.aggregate([{"$lookup":{"from":"SecondCollection","let":{"fieldname":"$FieldName"},"pipeline":[{"$match":{"$expr":{"$in":["$$fieldname","$Elements.FieldName"]}}},{"$project":{"SurveyId":1}}],"as":"SurveyInfo"}}])