What should a person who doubted having missed a pillar of prayer do?
All praise be to Allah, The Lord of The Worlds. The prayer of one who doubts having missed one of its pillars is valid, and nothing is due on him/her since having a doubt after offering the act of worship doesn`t undermine its validity. And Allah Knows Best.
What is the ruling on forgoing the sacrifice (uḍḥiyah) for one who is financially able to offer it?
Praise be to Allah, and peace and blessings upon our master, the Messenger of Allah.
It is disliked (makrūh) for one for whom the uḍḥiyah (sacrifice) is recommended (Sunnah) to forgo offering it, on account of the scholarly disagreement regarding whether it is obligatory. And Allah, the Most High, knows best.
Is Zakah (obligatory charity) due on land intended for selling?
Yes, lands intended for trade are valued, and Zakah is paid according to their estimated value after a lunar year had lapsed, but if the owner didn`t pay the due Zakah, then he should do so after selling them.
Is it permissible for the wife to give the Zakah (obligatory charity) of her money to her poor husband?
Yes, it is permissible for the wife to give from the Zakah of her money to her poor husband. And Allah Knows Best.