It is important for the questions to be grammatically correct, not to contain inappropriate language, and not to be repeated in the game.
You also need to take into account the region in which you place the question. Not all questions are global. In order to be so, they must be appropriate for any part of the world. Some questions are specific for a certain region, and this can be changed when suggesting the question.
Temporary questions can be rejected since they can change in the future. In order to guarantee that the question remains in the game, you can always add a time reference to it.
You cannot create questions that promote a certain brand. That will be considered Spam.
When suggesting questions, it is important to bear in mind that it is a family game, thus, they cannot contain any offensive content.