Where is you in the Hindi sentence? Can the personal pronoun be skipped in some cases?
The verb "जा रहे हो" makes it clear that the question is addressed to "तुम", and hence the latter can be omitted. It works pretty much like in Turkish, in which both "Nereye gidiyorsun?" and "Sen nereye gidiyorsun?" are valid translations of "Where are you going?"
Yes, it is also very common in Polish and other Slavic languages. However, it is the first time I see it in Hindi. So can one also say for example भारत जा रहा हूँ? Only मैं is used with हूँ so can one omit the pronoun? How common is it in Hindi?