"You are studying."
That is the Konjunktiv I form of the verb, you're looking for the present tense: "du studierst"
Note, by the way, for future reference in case it comes up that "studieren" means "to study" as in to study something at university or college level, like "I study law". "lernen" means "to study" when you talk about studying for an exam.
In this case however, when asked to translate "you are studying" into German, one could just as easily think of studying law as of studying for a math test. When no context is specified it should be accepted as possible answer.
You mean in German? ‘Lernen’ does cover both in most usages, yes, although only ‘studieren’ can be used for ‘studying at a university/attending university’ and ‘erlernen’ only means ‘to learn (thoroughly)’, never ‘to study’.