Database
[{Id:1,name:"p1",tasks:[{taskId:"t1",startDate:ISODate("2018-09-24T10:02:49.403Z"),endDate:ISODate("2018-09-26T10:02:49.403Z"),},{taskId:"t2",startDate:ISODate("2018-09-24T10:02:49.403Z"),endDate:ISODate("2018-09-29T10:02:49.403Z"),},{taskId:"t3",startDate:ISODate("2018-09-24T10:02:49.403Z"),endDate:ISODate("2018-09-27T10:02:49.403Z"),}]}]
Query
db.collection.aggregate([{$project:{name:1,startDate:{$max:"$tasks.startDate"},endDate:{$max:"$tasks.endDate"}}}])