Recently bought a home with detached casita its unfinished I notice no system ground at the sub panel switches have power but lights won't work. There is also no system ground on main house but lights are working there?

You don't need a ground for a circuit to work... unless that's what you're
referring to as a neutral or grounded conductor in which case you have some wiring to do. Are you qualified to do your own wiring?
Did you hire an inspector before purchase?