Question

how you can encourage your friend to give more importance to knowledge then marks

Answer 1

You can encourage your friend by telling him the importance to knowledge in the long run of life.
Knowledge is key of success and without it we can not do anything. Knowledge gives protection from many difficulties in life. It is batter than any treasure of the world. Knowledge guides a person to the right path in life.
While on other hand marks are a temporary milestone and whose value in life should never be compared to knowledge.

Answer 2

I'll tell him that marks can be obtained even a parrot can remember things but knowledge is the real thing which will describe you before world in the practical life. If a person has good grades but know nothing he can't secure a good job.