The drug in question is the widely known Modafinil, which I get in generic form from India. The gene is CYP2D6 [1], which I had checked by 23andme [2].
If you have the gene, when taken during the day, Modafinil allows you to focus for up to 12 hours straight, on the subject of your choosing (but you should choose something, or your attention span is wasted). With that focus, it is much easier to learn new things.
[1] http://youscript.com/healthcare-professionals/why-youscript/...