Do Ukrainian citizens require a transit visa at Vienna travelling form Ukraine to Serbia? [duplicate]

Did you look at the Austrian Consulate's web site? This is from http://www.bmeia.gv.at/en/embassy/consulate-general-new-york/practical-advice/visa-and-residence-permit/entry-permit-visa.html:

Passengers who are not visa-exempt under the Visa Waiver Program and travel from the US (or any other non-Schengen country) via Austria to another non-Schengen country do not need a visa, if they do not leave the transit area of the airport.

This is qualified by the next statement, but that applies only to holders of passports from the following countries:

Afghanistan
Bangladesh
Dem. Rep. of Congo
Eritrea
Ethiopia
Ghana
Iran
Iraq
Nigeria
Pakistan
Somalia
Sri Lanka
Syria

To make this a more generic answer: Transit visas at all Schengen airports are required for citizens of twelve countries (Afghanistan, Bangladesh, Dem. Rep. of Congo, Eritrea, Ethiopiam, Ghana, Iran, Iraq, Nigeria, Pakistan, Somalia, Sri Lanka).

Every country may add countries to this list for their airports. The list is long and in flux. Wikipedia has a list but in general, if you would need a visa (check with the IATA) to enter a country then call their embassy to check whether you need a visa for airport transit.

Answering the specific question is not possible since it does not contain the nation that issued the poster's passport. However, Austria -- at this time -- only adds Syria to the list of countries so if we suspect the poster to hold either an Ukranian or Serbian passport then no transit visa is necessary.