For example, omnipotence is a self-contradictory term, as you have a dilemma - if a being is all powerful enough to give itself limits, it is not omnipotent as it wouldn't be able to do the things it limited itself to do. Whereas if it can't self-impose limits, it's also not omnipotent as it isn't able to self-impose limits. Another example is that suffering exists in the world, which would be a contradiction if an all-powerful being that wanted to end suffering existed, since it should, but it isn't.
And these are just contradictions within God's character. If you want to look at the things he actually claims to have done, you'll find numerous more in the Bible. Just as one example, Jesus's last words are different in almost every gospel.