One of my friends is studying in Ukraine, now he wants to travel to India for vacation via Vienna. Does he require a transit visa?
No, he does not need a visa, provided he can stay in the international area of the airport (which means in particular that his luggage must be checked through to his final destination).
See also Do I need a visa to transit (or layover) in the Schengen area? for a full explanation of the rules. The most important thing is that India is not on the list of countries whose citizens require an airport transit visa in the Schengen area. A visa is only required to transit through Germany, France, Spain and the Czech Republic.