The quick answer, you should be looking at who you're talking to, so unless you're talking to the audience as in a Shakespearean soliloquy, you wouldn't look at the camera.
Almost always, when breaking the fourth wall (talking to the audience) is required, it will be mentioned in the script.
If not, it is an oversight and you can't do anything about oversights.
If you're still not sure, you can always get your agent to ask casting or if you don't have an agent, ask them yourself.
In an audition, if there is only one person to talk to, you can look at the reader or pick some other spot to look at as though it were the person you were talking to.
When there are multiple people in the scene, decide where they are and speak to them where you've placed them.
Some people would say you should ask the casting director whether you should look at the camera...
hmm.
I'm sorry, but that is bad advice.
That's like asking your editor if a sentence should be followed by a period.
If you don't know that, you have no business wasting anyone's time either as a writer or an actor.
If you have to ask something like "should you be looking into the camera", you are going to look like a rank amateur, which you obviously are since you are asking that question.
That is why you take audition classes, so you know the basics of auditioning rules and technique.
Seriously, producers are not supposed to be your teachers.
This is very basic fundamental knowledge and it is like going into court as a lawyer and asking if you have provide evidence or can you just use hearsay...
if you treat acting like joke, you are not only embarrassing yourself, but you make all actors look bad...
so don't do something you have never trained for...
take an audition class before you go audition.
It's not fair to the rest of us who are working our asses off.
If you had to ask in a THEATRICAL audition whether you should look at the camera, I'm sorry but you are an amateur...
You are basically telling actors it's OK to waste a CD's time by going in and not knowing what the audition if for.
If there is any confusion as to the type of audition, that is what your agent is for...
to call the CD and ask them, but if you don't know what type of audition you are doing when you walk into the room, you're dead already and it's likely only going to get worse because if you don't know who you are talking to, how can you possibly prepare an audition? The only question you should be asking in an audition is anything that is not clear in the script, and again that could have been taken care of by your agent.
If you don't have an agent, then you could call/email the CD yourself.
Either way, it shows lack of preparation if you are asking these questions 'in the room'.
Tacky and amateur.
Some people may wish that Hollywood was a touchy feely world in which things are 'okay' because they seem innocent but when you are trying to do something well and you start with an uneducated question you quickly find out how cruel Hollywood can be.
One, you will immediately lose credibility, and two unless somehow you rock their worlds after starting with a dumb question, you will never be called in again by that casting director (although if you don't know where to look in an audition, it's a wonder how you got called in in the first place unless the part called for a one-armed man or some other specialty you and few others possess), so why apologize for people's ignorance and not educate them as to how the real world works.
Acting is a profession which means they pay you for it, and people don't screw around when it comes to money, so show up prepared and if you don't know what 'prepared' means, then study the areas you don't know about so you never have to ask such rookie question.
Sorry but that's the truth, and all the sugar coating in the world won't change it.
There is ONE way to behave in a casting office...
BE PROFESSIONAL.
Asking questions leads to wishy washy auditions, which never book...
Better to get it totally wrong because then you are at least showing a new slant on the material.
An actor should walk into a room with their game face on...
chat with producers if they force you to but not about the script unless it is to compliment it.
Don't do anything that is going to throw you off what you walked in there to do...
full of beans and confidence...
not asking questions like you don't know EXACTLY what is going on.
You can be completely off the mark, but just go for it! Then if they want to see a different version...
and if you are confident and committed and they think you are right for the part, I guarantee you they will redirect you...
whether it is talking to the camera or taking it down a notch.
It's not always about booking, but showing that you put your all into your auditions.
Show your interpretation...
don't ask for theirs.
They really don't know what they want until they see it.
If they knew more, they would have written it down.
The only exception to this that I can think of is if you asked the question before hand and they never got back to you.
I cannot imagine a scenario where in a professional audition, if the script calls for talking to the camera, it would not be specified.
If it was overlooked, or even if you missed it, if you are good at your first pass, they will redirect you.
Student films are a different story and anything goes at an audition with amateur filmmakers, but again, ask before hand, not in the room.
That's a confidence killer unless you are Al Pacino and can come up with an entirely different take on the scene effortlessly.
While asking educated questions won't hurt you, there's no reason not to ask them before you get into the room, preferably days before if you receive the script ahead of time.
Think of it from the casting side.
You go to the trouble of providing a script and you expect actors to deliver their interpretation of that script.
The moment before they read, they ask you a basic/fundamental question about the performance...
that doesn't instill confidence in anyone.
In acting, there are no rules.
It is about interpretation and entertainment, and if you do something that was not in the script and the producers think you added value, they not only won't punish you for it, they will reward you by giving you the part.
The fewer questions you ask, the better.
Preparation is impressive...
uncertainty about the script is not.
If it's not in the script, logically fill in the gaps with the information that IS provided.
It is the actors job to bring an amazing, creative presentation of the material and once you start asking questions, you show you are not really prepared because if you weren't talking to the camera in your rehearsal, it is likely not going to be easy to incorporate it 'in the room' so despite what some people are saying, anything you ask seconds before you start reading makes you not only look unprepared but proves that you are unprepared because if you are making an adjustment on the fly, it has the potential to interfere with your preparation/characterization...
talking to camera is a major adjustment of character...
almost always involving changing character from the one in the scene to one who is talking about themselves like is often done in cartoons...
a wink to the audience so to speak.
So despite the desire for people to get their point across, you are only hurting actors chances by advising things like 'ask questions'.
You're not there to ask questions, but to deliver a performance...
so do that to the best of your ability and if they want to see something different, they will tell you.
You're not going to lose the job because you did something slightly different from the writing.
You're going to lose it because you aren't working from a place of total commitment.
Bonus information- What to do when a casting director redirects you incorrectly.
I have received scripts that i could tell were comedic by how slightly outrageous they were, but the casting director either didn't read the script (I hope that's not the case) or they just don't get comedy unless it says COMEDY on the front page.
So I did my interpretation which I knew was the writer's intent and they redirected me to do it without the comedy and if the writer/producer is not in the room, you're screwed.
What are you going to do? Argue with the CD who just by being behind the camera thinks she is right.
The smart thing to do is to decline the second read because you just gave them you're best read.
Casting often tries to get actors to do 'what is expected' and drag actors away from their choices because they simply don't understand the script or the actors interpretation of the script, even if it makes perfect sense.
They really have no business doing this and should be letting actors survive or fail on their own swords because they don't have the final say on who gets the part.
I've run hundreds of producer sessions and sometimes the CD agrees with the producer and sometimes they don't, but they don't write the checks so if they haven't been specifically instructed on a choice, they should not sabotage actors who might be nailing the read, only to be dragged back to the middle for lack of understanding of the material.
Of course, I could be wrong.