Once licence is copied to USB dongle, it cannot be copied to Soft-licencer, not on main computer, not transfered through second USB-licencer to any other computer. That’s the reason we use dongle - antipyracy.
And I have the same situation as you. When I was on Elements 8.5, I bought Padshop, then upgraded to Padshop Pro. Then upgraded to Cubase 9.5 Pro and had the same Padshop Pro. Now I upgraded to Cubase 10.5 which have new Padshop 2 and I want my Padshop Pro licence transfered to my son’s computer. It’s difficult. Right now I’m waiting for support from Steinberg. I will post here if we found a solution.