You can reports players here: https://reports.cubecraft.net/report Here are the guidelines: https://www.cubecraft.net/threads/player-reporting-guidelines-and-formating.136047/ You can upload your evidence to YT.
Read this because not all the reports require the same evidence: https://www.cubecraft.net/threads/player-reporting-guidelines-and-formating.136047/ And you can report a player here: https://reports.cubecraft.net/
It's your first time reporting a player? Then join Cubecraft server and in a lobby type /registerreports after that click what appears in the chat :)