Its been close to oer a year since I have played ffxiv. I recently decided to resub and I am leveling an alt on a char I have already hit 50 on.
My question is, since the main story line has been extended since I last left, how can I check what my progress is so I can continue when this alt class hits 50???
You can go into your journal ("J" on pc) and check completed quests in main story. You can turn in new quests post 50 on any appropriately leveled job.
The easiest way is to remember the time you went off. If you went off say Patch 2.1, then check out Patch 2.1's patch notes against your Journal to see if you completed everything, if not, follow it through and then move on to the next following patch notes. The patch notes gives you the starting points (coordinates and name of the NPC) that gives you the relevant quests to move on.