Do Trainers need training? Yes of course they need training, but they do not need to be trained. This is what makes them Trainers at the cutting edge.
Obviously, if they need to be trained, then they are the learner. If a trainer believes they have outgrown the learning stage, they are actually doomed as a trainer. All trainers worth their salt accept that they need to keep learning constantly, just to keep pace with the rapidly learning youngsters who will ask them questions during their training sessions. The better trainers learn faster than anyone else. It’s just that simple.
So how do Trainers learn so quickly? What do Trainers do to learn without being trained?
Trainers are experts at focusing on learning objectives and asking questions, assimilating answers, and practicing without inertia. This expertise of asking questions is the expertise knowing which questions to ask, how to ask which question, who or what to tap for the answers, and what questions need to be answered first. This expertise naturally gets them the answers before anyone else, and that is what creates the opportunity for them to be Trainers.
Trainers develop the ability to assess the purpose for every piece of information. While good learners need to know how to answer all the questions they are presented with, good teachers need to be able to reverse-engineer the questions from looking at all the information (‘answers’) that they perceive. Trainers have to be able to determine the objective from the response. And, the best trainers are able to ask new questions, questions they have never been faced with.
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Mukul's Blog 
Very true. Learning is a never-ending process.
Not only is it never-ending, it is the only way to move ahead.
A good analysis. The very important quality of a good trainer is forcasting likely questions and preparing answers for them in Advance. So in a way training is required for trainers in aquiring this skill.