The 'training' part of the program is of course mostly about 'remembering' what you have already at some point decided to be the proper course...so that you will have indeed committed it to memory for future game situations. So you have already...or should have already toyed with 'reasonable moves' prior to this point.
So, in that sense, I would disagree that there is truly a common idea here between what you and I suggest. You - if I understand you right - essentially want to test out new moves while in training...while, in training mode, I just want to train but think something to prompt you - like the 'threat button' I discussed, is reasonable within this mode. I mean, if you do not get the move right, you don't know it. Simple, you have not committed the position to memory and need to do something to make sure you do have it in your memory in the future...like during a game.
Of course a 'threat button' would just be what the engine calculates as your opponents move if you 'passed', but a lot of times it would of course point you to what you should be doing here...as if a coach was looking over your shoulder when you get stuck.
But maybe Stephan can decided which is most appropriate here.
The other suggestion...I've mixed emotions about as it relies on the quality and how up-to-date that database is. And who really wants to find the only move in a given position was played by a 12 yr old school girl rated 1247 in Brazil? The quality of the database would be everything here.