Each mark requires its own test.
The Mark of the Scholar is reserved for those who pass the Trial of the Scholar. You must be above level 35 to qualify. To take this test visit Magister Mirien in the temple of the Town of Dion.
The Mark of Trust is reserved for those who pass the Testimony of Trust. You must be above level 37 to qualify. To take this test visit High Priest Hollint at the Town of Oren.
And last, the Mark of the Magus is reserved for those who pass the Test of the Magus. You must be above level 39 to qualify. To take this test visit Bard Rukal of the Town of Dion.