Class Keys - How to use?

MiguelRealPT

How or where in the game can we use the class keys?

SummonerNR

Do you mean the Gate Key ones from Act-5 (or was it 6) ?
That you had to find in other quests there, then go use them in different quests of that Act.

They removed their gates for good, after so many issues of people having them lost, etc, and unnecessary anymore as future ACTs made that one more low-level.

But you probably still have the ones you never used still in your Inventory.