To get the Wax On, Wax Off achievement in State of Decay 2 do the following:
You max out skills by putting them to use. Fight (using melee combat) enough with a character and they'll eventually max out the first-tier fighting skill and you'll be able to choose a specialization on top of your previous bonuses.
Access that menu by pressing down on the D-Pad, then LB to look at your skills. Pick one of the two seemingly randomized specialization skills and the achievement is yours.