Questions and questioning techniques are one of the most important aspects of training. How are you going to know if the trainees have understood what you are saying if you don't ask them? Why do you think there is a written paper for forklift truck operators?
There are basically two types of questions: real or rhetoric. A real question is where one expects an answer and a rhetoric one is a question where no answer is expected.
REAL question. What should you do before operating the hydraulic controls on a forklift truck?
RHETORIC question. Have you all heard of the Health and Safety at Work Act?
Avoid asking any question that can be answered by the words "yes" or "no". An example: Do you understand Einstein's theory of relativity? Assume someone answers "yes". How do you know if they really know it? Better to ask them what the formula is.
HOW to ask questions. There is a technique to this known as the three Ps. Pose the question, Pause to allow them to think, Pounce on someone.
If you nominate a person first, the others don't have to think about it. By asking the question and then picking on someone, everyone has to think about it!
If you don't know the answer to a question you have been asked don't try to bluff your way out of it. The questioner may already know the answer and wants to see if you do. Instead, apologise for not knowing and promise to find out. Make sure you keep your promise.