I don't think there's a way yet to allow players with the right permission to see the predefined reasons in reasons.yml ingame.
They'd have to refer to a guide/list outside the game, like on a forum or Wiki.

-bm.command.reasons
/reasons would show the list of predefined reasons.

Available predefined reasons:

• #abcdefgh = Some profound text here.
• #ijklmn = Commonly used for integers!
• #morereaons = Last one for this issue. It even has a flag! -p 1000 (not in yet)