Hi,
If you would have both licenses on the same USB-eLicenser (or both USB-eLicenser would be plugged in – with Nuendo 10 and other with Cubase 10.5 license), then you would see Padshop 2 in Nuendo 10 too. Same as you can use Padshop 2 in Cubase 9.5, if you have Cubase 10.5 license.