Translation:I take notes on paper.
As of December 20th, 2018, it appears to be the default translation.
EDIT April 17, 2019: Never mind. The default is now "I TAKE notes on paper".
I think you're right. "在" is used to express present perfect if there is no other use of it. In this case "在" is used in conjunction with "上" meaning "on (paper)". That means that this sentence should be translated as a general habit and not as an action.
Is it a specific piece of paper? In which case it would be 'the paper'. If it is paper in general it should be 'on paper.'
For a sentence describing a general habit you use "write notes" not "write the notes".
We don't usually say writing notes on a paper. Either on a piece of paper or on paper
Since it's not 一张纸 it's just paper not a piece of paper. Same goes for the notes, no measure word so no indefinite article and the sentence is general not specific.
Wait, so the 在 doesn't automatically mean "in the process of?" i.e., I am writing notes on paper? I'm so confused.
i guess 在 should be translated by present prefect. I'm writing notes on a paper.
No I was confused by the sense of 在. In this sentence it has nothing to do with the present perfect, but it is 在....上 (on). But finally who knows, i mean how would you express the present perfect in this sentence. Could be 我在纸上在写笔记。or 我现在在纸上写笔记。