Is there anyway to propose a puzzle for training? I have a few I'd like to suggest.
It's not possible, because the training puzzle come from game analysed by stoktfish. More information here :
http://fr.lichess.org/blog/U4sjakQAAEAAhH9d/how-training-puzzles-are-generatedIt would also be possible to just run a position through Stockfish. There are some really cool puzzles out there. One particular one I have in mind takes Stockfish a few minutes to see.