Can he think of a riddle that he couldn't solve himself?
Can he create a boulder so heavy that he can't lift it himself?
If yes than he isn't all-powerful because he can't solve the riddle/lift the boulder and if no, he also can't be all-powerful because he can't create it in the first place. Thus, since this can be applied to any property a god is claimed to be unlimited or all-powerful in, all religions that claim that their God is all-powerful or all-knowing in any way are invalid.
Can he create a boulder so heavy that he can't lift it himself?
If yes than he isn't all-powerful because he can't solve the riddle/lift the boulder and if no, he also can't be all-powerful because he can't create it in the first place. Thus, since this can be applied to any property a god is claimed to be unlimited or all-powerful in, all religions that claim that their God is all-powerful or all-knowing in any way are invalid.