Admin Danger Zone is one of the server administration windows. Open it from File > Admin; it opens as a desktop window you can drag, resize, minimize to the taskbar, and close with its title-bar X.
What a wipe removes
The preview lists what /admin nuke would delete. Admin roles, audit logs, server bans and server settings survive it, with registration reopened so an admin nick can be recreated; everything else does not. This cannot be undone.
The confirmation
The button stays disabled until you type the server's current name. The server checks the same thing when the form is submitted, so a stale button is never what authorizes a wipe — if the server was renamed after the preview loaded, the submission is refused.