кадом

Нӯшокии дӯстдоштаи тоҷикон кадом аст?
Which is the favourite drink of Tajiks?
Имрӯз кадом рӯзи ҳафта аст?
Which day of the week is it today?

Bonus:
Кадом can also often be translated as “what”.

кадом вақт: what time
кадом рӯз: which day
аз кадом шахс: from which person; from who
аз кадом тараф: from which side
ҳеҷ кадом: none, not one (for example, none of them)
ба кадом сабаб: for which reason; why