Welcome back!

You will probably figure out the new stuff yourself, the game is good at holding your hand. You can turn on "Recommendations", which will show a list of quests and other things for you to do.
Some of the old stuff that is not quite as you remember it might be confusing, or you might be looking for something that no longer exists. Here are some of the things that may surprise you if you haven't been keeping up:

You must redo all your class quests. You must also redo all of your job quests. If you or your Calamity Salvager is carrying AF gear, wonky stuff can happen with multiple copies of the same U/U item. Jobs are now mandatory if you want to do anything past level 30, even if the game never tells you this. People will most likely be mad at you if you join something as CNJ50.

Depending on when in 1.x you're from, CNJ might have changed significantly. It is now purely a healer class (and WHM a healer job), not a vaguely astral-aspected all-round mage. Gone are the days of farming guild marks to make your own class. Instead, you get "role actions" which for CNJ (and WHM) will be from the healer category of role actions. There is also no physical level and skill level, the levels are per class/job now. All gear has a required minimum level, the optimal levels are gone. You get EXP only, no SP. The armoury system has been restricted, now you can only change jobs outside of duties.

Don't be afraid to attempt content labeled "Hard" with random parties through the duty finder, like I was. They are a joke compared to the 1.x hard trials.