Trial key SKills

Was wondering if i add a cd-key for NF on my account and if i unlock a skill with i keep it ?

nope, once the trial ends it will become "locked". you won;t be able to use it again untill you purchase NF, however you won;t have to buy it again.

Yes and no. Skills from other campaigns unlocked during the trial period will remain "unlocked" in the sense that once you add the retail campaign key, you won't have to unlock them again. However, you(neither your PvE or PvP chars) will not be able to use them(different kind of locked) until you add said retail key.

Your Heroes, however will still have access to those skills.