Database
[{roomId:"id",questions:{q1:{user1:"user1's work",currentQuestion:"currentQuestion1"}}},{roomId:"id",questions:{q1:{user1:"user1's work",currentQuestion:"currentQuestion2"}}},{roomId:"id3",questions:{q2:{user1:"user1's work",currentQuestion:"currentQuestion3"}}}]
Query
db.collection.update({"roomId":"id","questions.q1.user1":{$exists:true}},{"$set":{"questions.q1.currentQuestion":"new question"}})