To ask questions when you already know the anser

I do it to learn about the person I’m talking to.

Cross referencing and whatnot.

Sometimes I do this because most people like to be listened to and to have the feeling that they are teaching someone something. I do this with people who I've just met and I want to be friendly with. It's never good (for relationship) to be seen as the all-knowing one.

So depending on the circumstances it might be a good move. And when you have children you do it with them very often.

In certain cases it is normal to do so. A person will ask such a question to be sure that the person being asked knows the answer.

It's surprising how many times that "trick" makes people aware of their situation at the time. Many people are blissfully unaware of many things going on - and even about themselves.

By asking such a question you often force the person being asked to evaluate and provide the answer, and at the same time realize that they have been acting wrongly on something. Thus, they change their actions.

Now if they are totally clueless after being asked.. they are likely distressed to the point of being unaware of what is going on, sick, or just in the wrong position or situation for them.

Then they should be required to take time off and recover, or gracefully scheduled into more training, or gracefully transfered to a position they can handle.