Helping TA's creativity when writing exercise sheets
I'm not sure why you find this to be a special problem. We basically know how to teach people things. Just do it in the ordinary way. 

If no framework for understanding how to do a task exists then you need to develop one. If you know how to do it, but are unique, then you need to capture what you do in some way that can be transmitted. 

Then you "teach" it by presenting the framework and giving some exercises so that it can be practiced and giving some feedback on how people do. 

It is a standard teaching problem. 

If no one knows how to do it, then you need to do something like research to discover how it can be done and then operationalize that research. Again, a standard problem, with a standard solution. 

But, one thing I would suggest is that you use some sort of team learning so that those who do it naturally can pass skills to those who struggle with it. Pairing is a good approach and one I often recommend for such tasks. 

Beyond that, it will likely take the examination of good and bad examples, using discussion (by the TAs) of why some things work and others don't. 

But it is practice and feedback that are the key to learning almost anything, hence key to teaching it. 



Don't take the word "framework" too literally. 

Also, the task itself is ill defined here. Expect that no one will be perfect at it and that the "examples" created will sometimes fail. But there are ways, such as pre-testing or other evaluative methods, to deal with that as well.