Database
[{"_id":"a","lastName":{"lastName":"James"},"data":[{"day":"20-09-2020 11:35:02","hoursWorked":"0 hours : 5 mins : 321 secs"},{"day":"20-09-2020 11:35:29","hoursWorked":"0 hours : 5 mins : 321 secs"}]}]
Query
db.collection.aggregate([{$project:{"data.hoursWorked":1}}])