I have a Cu EL9 and i baought a new Cu pro 10

Can I run both at the same time?
and also do I have to run the Cubase 10 with a USB licenser?

Hi and welcome,

Yes, these are 2 independent applications. If you bought a new license, you are owner of 2 licenses and you can use it on 2 computers simultaneously. Or you can keep Cubase Elements for case when you don’t want to use the USB-eLicenser at the computer.

Yes, the USB-eLicenser has to be always plugged in, when Cubase Pro is running.