In The Walking Dead Survivors game there are two types of exp, namely survivor exp (combat) and Survivor exp (development)
How to obtain survivor exp
Attacking zombie walkers and Woodbury Army will give you some survivor experience. Over 17k exp from lv 10 woodbury.
Buy books at lone trader, The lone trader sells a lot of items. Sometimes lone trader stores sell exp and shield books.
Get books from radio gacha You can get exp booster books from the radio.
Get survivor experience from events such as the Survival Challenge event, tides of the dead etc.
Assign development-type survivors in buildings such as worker cabins etc to obtain exp