How do I route a USB instrument into Cubase?
Not sure what you mean.
I use a USB cable (coming from whatever USB device) connected to a USB port on the computer.
Or did you mean something else;
like routing the ‘audio’ from an outboard USB instrument into Cubase?
An outboard piece of equipment.
I have a digital dj usb instrument.
Then it should be able to plug directly into a USB post on yer 'puter.
For Cubase to ‘see’ it, you might have to install specific ‘drivers’.
Check with the makers of that device, and ask if drivers are needed;
and if so, do they have drivers that are compatible with your OS and Cubase?