Database

[{"_id":ObjectId("636efe231eeef2f46a31d7f4"),"sName":"Somu Nelavalli","class":"tenth","year":2003,"studentMarkDetails":[{"examType":"quaterly","marks":{"Eng":55,"Tel":45,"Mat":75,"Sec":43,"Soc":65}},{"examType":"halfyearly","marks":{"Eng":56,"Tel":76,"Mat":89,"Sec":34,"Soc":76}},{"examType":"final","marks":{"Eng":89,"Tel":78,"Mat":91,"Sec":95,"Soc":87}}]}]

Query

db.collection.aggregate([{$unwind:"$studentMarkDetails"},{$project:{"sName":1,"class":1,"year":1,"examType":"$studentMarkDetails.examType","total_marks":{$reduce:{input:{$objectToArray:"$studentMarkDetails.marks"},initialValue:0,in:{$sum:["$$value","$$this.v"]}}}}}])

Result