db={"users":[{"_id":"4775222e-8e4f-4f84-8dba-b097291bbd39","surname":"Smith","forename":"John"}],"job_requests":[{"_id":"f4bdda3e-0e8d-4e8d-b070-7d01421f5a51","description":"do something","riskManager":{"$ref":"users","$id":"4775222e-8e4f-4f84-8dba-b097291bbd39"}}],"jobs":[{"_id":"nekiID","description":"do something","jobRequest":{"$ref":"job_requests","$id":"f4bdda3e-0e8d-4e8d-b070-7d01421f5a51"}}]}

db.jobs.aggregate([{"$lookup":{"from":"job_requests","localField":"jobRequest.$id","foreignField":"_id","as":"jobRequest"}},{"$unwind":"$jobRequest"},{"$match":{"jobRequest.riskManager.$id":"4775222e-8e4f-4f84-8dba-b097291bbd39"}}])