create a test with at least one
1) Multiple Choice, Single Correct and Enable Negative Points option. Make the points for answering correctly 10, and points deducted if wrong to 2.
2) Add at least one other question of any type which is automatically graded (just to save you some time) and give it 10 points.
3) Publish the test
4) as student take the test and answer the one with Negative points incorrectly and the other question correctly. Submit.
5) Submit the test as student.
6) As instructor, check the score for the student.
Result: The points awarded for getting the question wrong is zero instead of -2 , points deducted for getting it wrong.