Honestly, I think "DM training" could deal with topics like "What to do about a disruptive player". "Help, I let a player use a broken class/gave them a broken magical item and it's ruining the game; what do I do?" "How do I make adventures/dungeons/exciting encounters?"
And just provide general tips and tricks.
For instance, I was talking to a new player and he gave me some awesome advice. He said that when he DMed, he'd give the PCs a sheet that listed several notable NPCs, each with a blurb beside them. This list was "What you could find out with a basic Gather Info roll". Like "Helga owns an Inn, but for a fee, she will hide you if you're hurt and in trouble." "Boris is a cheap, honest fence; he won't move anything high priced or rare stolen goods, but he knows people who will." The downside to this list is, anyone can find this out, so the Guards know that Helga hides people, and they will stake her place out, etc.
This way, if the PCs are in need of something, they look down at their paper and go, "Hey, can we get ahold of Helga?" "Sure can."
And just provide general tips and tricks.
For instance, I was talking to a new player and he gave me some awesome advice. He said that when he DMed, he'd give the PCs a sheet that listed several notable NPCs, each with a blurb beside them. This list was "What you could find out with a basic Gather Info roll". Like "Helga owns an Inn, but for a fee, she will hide you if you're hurt and in trouble." "Boris is a cheap, honest fence; he won't move anything high priced or rare stolen goods, but he knows people who will." The downside to this list is, anyone can find this out, so the Guards know that Helga hides people, and they will stake her place out, etc.
This way, if the PCs are in need of something, they look down at their paper and go, "Hey, can we get ahold of Helga?" "Sure can."