Is it possible for a sufficiently clever human being to somehow mislead/trick/fool God? If so, how could they do it? It seems like God's omniscience/omnipotence would preclude that, but perhaps there is a loophole somewhere. (We'll assume a scenario where the God that exists closely resembles the one described by the Christian faith)
My child walks into the room and asks me, "why did the chicken cross the road?". Recognizing my child's age and the fact that this is the first jaywalking chicken question that he has ever asked me, I'm pretty sure that I know which answer he is going for; but I play along.
"I don't know. Why?"
A few moments later, my child runs off, overjoyed that he "tricked" Dad. Meanwhile, I sit back and quietly laugh, finding far more joy in my child's joy than I could ever have gotten by defending the omniscience which he still believes that I have.
So, yes. From the viewpoint of one of the created, trapped inside of creation, we can apparently trick God and prosper from His loving response. Just don't fall into the trap of believing that you've actually pulled one over on creation. ...and never try the same joke twice. Omniscience means that God knows an almost infinite number of ways to turn a punch line against you.
In one of my stories, Magic is real and nearly infinitely powerful; capable of overpowering almost any physical law. The secret of that magic lies in making God laugh. If you can write a really funny joke, and then set up all the props and players just right within the real world, and if you are lucky enough to catch God in a particularly playful mood, then all of creation will bend to your will, pulling off the punch line, no matter how many improbable or impossible things have to happen to make it all come true.
God's Laughter! Now that's Magic!
That depends on what you mean by "trick". If you mean mislead then no you can not, unless you find a way to block his omniscience, Im not sure how this would be possible but it your world so I am sure you could come up with something. (maybe some kind of spell, or some kind of super machine)
If by trick you mean keep him from doing something then that might be possible (very unlikely but maybe) If your thinking of Christian, Jewish and Muslim God then not only is he omniscience but he can't lie, or take back his words and promises. You could get him to agree to something that would hinder his actions sometime in the future. Of course since he can see the future you can't trick him this way without him allowing you too. Perhaps he would do it if in the long run your trick served a high purpose or if he was so impressed by your audacity to try and trick the almighty that he just decide to let you get away with it. Of course if that is the cause then may He is secretary tricking you.
Also if you could some how convince God put aside his powers and knowledge to enter some type of competition with you (Kind of like the time Israel/Jacobe wrestled with God) . Then on a more equal playing field you might be able to trick him and win the competition.
Consider instead the concept of "knowing God's true name". I'm not sure about the Christian (Jewish) God suffering from this in any apocryphal stories or even hypothetical literature, but in many stories dealing with spirits and demons, knowing the creature's true name gives you power over it.
I don't have time now to fully expand this answer here, but it would basically be a repeat of this answer I wrote on Christianity.SE.
So in your story your character could learn God's name, then trick him. Though it may be more fun if he tricks God into revealing his name himself, but then we're back to square one. How would he trick an omniscient God?