Which vpn or socks can I use as exit node from Tor in Kali?
socks chain is transparent(not encoded). Most bad design tor->socks, socks->tor looks better. So tor->vpn better design. When you use tor->socks->socks...->socks then last tor node know all about your socks chain going next.
As far as I understood you, we can't use any vpn over TOR(which given by gateway) in whonix workstation?Sorry dude but you can't use VPN over TOR, only VPN->TOR, for more specific information look on official whonix page about different chains anonymity.
In this case - we can't. In another system - yes. But it's not good decision cause this established connect will be often destablished. Anyway, all depend from your goals.As far as I understood you, we can't use any vpn over TOR(which given by gateway) in whonix workstation?
We can.