Guild Wars 2

Any way to tell which paths have been completed for a specific dungeon?

Do you need to complete all paths of a dungeon with the same character?

Question 1: No, nothing has been implemented. You just have to remember.

Question 2: No, you can mix and match characters for dungeon master title. As long as each dungeon path is run, (including story mode) you will get the dungeon master title.

I’m asking about completing a specific dungeon, let’s say I did Story, path1 & 2 of AC with one character, then did path 3 with a different character, will that still complete AC?

Yup.