If you have a set of specific things to monitor that aren’t in an existing management pack, you need to create a custom management pack. You especially need to create a management pack if you want to apply those monitors to multiple devices.
To create a management pack in SCOM 2012:
Open the SCOM 2012 console
Click on Administration
Expand Device Management
Right click on Management Packs
Click Create Management Pack
Enter the name of the management pack that you want to create
❗ Disclaimer: I have no idea what Knowledge does
You have no created your management pack, you are free to add monitors to it and apply it to devices to be monitored.