[{_id:1,lodging:{reviews:[{cleanliness:0,location:0,food:2},{cleanliness:3,location:4,food:5}]}},{_id:2,lodging:{reviews:[{cleanliness:5,location:5,food:5}]}}]

db.collection.aggregate([{"$addFields":{"sumPoints":{"$reduce":{"input":"$lodging.reviews","initialValue":0,"in":{$sum:["$$value","$$this.cleanliness","$$this.location","$$this.food"]}}}}}])