I do not think that you can get this info as a nice column in the 'Results / Grades' report you are referring to. However, if you click on an individual mark, a window will pop up with a 'Completed date' that is the date the question was graded, whether it was automatically by Moodle when the student submitted the quiz or manually by the trainer.
If you go to 'Grades / Grade history', select the 'Grade item' and the 'Grader', and click on the [Submit] button, you get a table in which the first column, 'Date and time', contains the date and time at which the quiz was graded by the trainer. If you select 'All graders', you get both the time when the quiz was automatically graded when submitted by the student and the time when the trainer updated the quiz grade, by manually grading a question or by revising the mark for any other question. If you play a little with this table, you will find it easy to understand what it displays.