Si os veo copiando, os pongo un cero, os quito 2 puntos

[ROBINDESBOIS]

How can I translate that?
If I catch/see u copying I ll give you a zero/ I ll take 2 points off of your final mark.?

[Rusty]

If I catch you cheating (copying answers from another, as well as getting the answers beforehand and bringing them to the test), I'll give you a (big fat) zero on the test.
If I catch you cheating, I'll immediately confiscate the test and you'll get a zero.

One's mark is used in the UK. In American, we say grade.
Your grade will be (a) zero if I catch you copying someone else's answers.

[JPablo]

Thank you, Rusty.

And what about the "os quito 2 puntos de la nota final" (the average final grade)?

[Rusty]

Taking two points away from a grade doesn't "translate" for someone like me who is unfamiliar with the grading systems used elsewhere. So, I took no stab at a translation.

[Perikles]

(UK response)

It depends a little on whether this is an isolated test or part of an exam which involves several tests. If just one test, the result is a mark. If part of an exam which sums the total marks of several tests, it might still be a mark, or could be translated into a grade.

Anecdote: at school I had an old-fashioned Latin teacher who used to deduct marks from tests for bad behaviour. The tests were usually 20 questions and you had a mark between 20 out of 20 (20/20) and zero out of twenty (0/20). Except that once I got all the questions wrong, and he deducted 3 marks for bad behaviour, so my final mark was minus 3.

[JPablo]

My goodness! That must be a record score...