What skills and training would any of you deem essential for a trainer? I.e. qualifications, skills, training for a trainer, certifications, etc. (Maybe we can derive a general common list out of this)?

My personal opinion is that a trainer should be  strong in practicing empathy and problem solving skills so that they can identify and understand the 'actual problem that's there' and have a 'solution that's relevant to the participants and their reality'.

This has always dictated my homework/preparation and content development process and has helped me create engagement during the sessions too even when my public speaking skills are 'just average' and I've seen more certified trainers and excellent public speakers struggling with engagement or/and staying relevant. 

Companies mostly don't invest much in post training anchoring of  behavior change that in my opinion impacts the long term results. And without that I personally believe that no training can bring a behavior change in the long term. 

There's an excellent book called 'know can do' on this that I would say all trainers must read.