Is vomit among the nullifiers of Wudu (ablution)?
Vomit does not nullify Wudu, but it is a Najaasah (impurity) that requires rinsing the mouth and washing whatever became dirty by it since the prayer becomes valid only after the removal of Najaasah. And Allah Knows Best.
What should a person, who doubts the validity of his Wudu, or over performs it, do?
One who doubts the validity of his/her Wudu while performing it should redo it until he/she is certain of having attained purity. But, if doubt was after having performed Wudu, then he/she should not pay attention to that as doubt after the end of an act of worship does not count. This is of course in case doubt was within the reasonable limits since once it goes beyond that, it becomes a whispering of the Shaytaan (devil) which he/she should ignore as the Wudu is valid.
Can a woman perform I‘tikaf in her home?
No, a woman's I‘tikaf is not valid if performed at home, because her home is not a mosque.
How is Laylat al-Qadr observed?
Laylat al-Qadr is observed through various acts of worship and obedience, including:
● Performing obligatory, Sunnah, and voluntary prayers
● Reciting the Quran
● Increasing remembrance (dhikr) of Allah
● Giving charity
● Performing I‘tikaf
● Inviting others to Allah
It is also Sunnah to increase in supplication and humbly beseeching Him, Glorified and Exalted be He.