Nudge is an application to notify end users about macOS security updates they should install - when a new security update for macOS is released, users of macOS devices will periodically receive a popup notification.
Clicking Update Device in the upper right of the popup will take you to the Software Update dialog box.
You can also go there by clicking System Settings... (2nd item in the  menu in the extreme upper left of your screen), selecting General in the lefthand pane, then selecting Software update (2nd item from the top in the righthand pane).

If your Mac is capable of running macOS14 (aka Sonoma), you will see the option to Upgrade Now to Sonoma at the top of the Software Update dialog box.
Please do NOT click on the Upgrade Now button - CLASSE Macs are running software that is not yet compatible with macOS 14 (Sonoma).

If you scroll past the rather long text description of Sonoma, you will probably see something similar to:

Clicking on the blue More Info... text should bring up a dialog box similar to:

CLASSE IT recommends installing updates like these.

Note: Apple is calling minor system updates Updates and major system updates Upgrades.