My familiar has commune.

[Titania, the Summer Queen]

Considering a strict DM, what are six questions to ask?

[Falcar]

I am assuming an Imp as that is the only familiar off hand that i know who has that but it depends on what needs an answer. Who hired the assassins? is the king trustworthy? is the advisor trustworthy? are my friends trustworthy, which direction is the nearest tavern? most any question that a short answer will help, this greater being will not lie to you but if it is the imp it might try to trick you or manipulate you into evil.

[tonyz]

Quite a few improved familiars have commune (cassian angel, silvanshee, arbiter inevitable, imp, quasit, maybe some others I don't know about).

What to ask -- depends very, very much on the situation. You have to know enough about what's going on to ask the right questions.

[Paladin of Baha-who?]

Pretty much all the outsider improved familiars have commune. Yes or no questions only, of course, but part of it requires knowing your GM.

For instance, "Is the King trustworthy" is a question that a tricksy GM may distort. He's very trustworthy -- to his allies, who are the Church of Asmodeus.

Questions that can't be easily distorted work well. "Is the king a genuine ally of the church of Desna" is a good one, for example, or "Were the assassins hired by the king or an agent, direct or indirect, of the king?"

The exact questions, of course, depend on the scenario you're facing.

In good GM hands, this spell is basically, "Hey, Mr. GM, please railroad me a bit so I can figure out what to do."

[Shalafi2412]

It also depends on the type of familiar you are asking as well. I would not trust what an imp or quasit.

[Titania, the Summer Queen]

The familiar is a lyrakin azata.

[Lincoln Hills]

The prior advice about your questions varying depending on the situation is fairly solid... And as Shalafi2412 just indicated, bear in mind that even if the entity answering the commune answers honestly (not guaranteed), you're still reliant on the familiar reporting that answer honestly. An azata and her supervisors want Chaotic Good to flourish: they might not lie to you (at least not if it would lead to you suffering harm), but they might omit things or shade their answers to prevent you doing things that might lead to a sudden ascendance of law or evil. Even more likely, their own perspectives can lead to some inhuman judgements on what is 'good' or 'desirable', so try to use practical and absolute terms when you phrase your questions rather than asking them to judge things.

Use the answers you get to make plans, by all means, but you should never hinge your survival (individually or as a group) on information you receive directly from the spell - and even less so on information you infer after your group yaks about what the commune answers meant.