question
Is paying khums obligatory on my wife’s dowry? For instance, is paying khums obligatory on dishes kept in showcase that may not be used?
Concise answer
According to most of maraja’, since dowry is considered as gift or it will be used in the future, payment of khums is not obligatory on it. However, it is regarded as those things on which payment of khums is obligatory, according to some of maraja’[1].

Appendix: The grand maraja’ answer regarding this question is as follows:[2]

Grand Ayatollah Khamenei (May Allah grant him long life):
Paying khums is not obligatory on dowry.
Grand Ayatollah Makarem Shirazi (May Allah grant him long life):
Khums is not obligatory on those things which are usually regarded as necessities of life, though they have never used yet.
Grand Ayatollah Sistani (May Allah grant him long life):
Yes, Khums is payable on it.
An answer given to the question by Ayatollah Hadavi Tehrani (May Allah grant him long life).
No.

[1] . Ayatollah Sistani (May Allah grant him long life).
[2] . This question has sent to the office of grand Ayatollahs: Khamenei, Sistani, Makarem Shirazi (May Allah grant them long life) by IslamQuest Website.