In England we have an idiom for this: 'brownie points'. 'Timmy got loads of brownie points from teacher for the painting he did'. More formally, plus point is fine. Or 'tick'.

I do not know where minus point came from. The way we normally say it in English is to lose points. When you succeed, you gain points.

Or you can say he received credit for a correct answer.

Yes. It would be plus point.