What is the ruling on someone who intends to travel to Jeddah for two days — must he enter iḥrām from his place of residence [i.e., before passing the mīqāt]?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah ﷺ.
Whoever is firmly resolved in his intention to perform ‘Umrah before setting out on his journey, it is unlawful for him to pass beyond his country's mīqāt (the designated boundary point for entering the state of iḥrām) without entering iḥrām. If he does so, he must return to the mīqāt to enter iḥrām from there, provided he has not yet begun performing the rites of the pilgrimage — in which case nothing further is required of him. However, if he does not return, he must offer a sacrifice (sheep/goat), to be distributed among the poor of the Ḥaram.
It is stated in at-Tanbīh fī al-Fiqh ash-Shāfi‘ī (p. 71): "Whoever, intending to perform the rites [of ‘Umrah or Ḥajj], passes beyond the mīqāt and enters iḥrām only after it, must offer a sacrifice. However, if he returns to the mīqāt before beginning any of the rites, the sacrifice is waived from him."
Accordingly: whoever is firmly resolved in his intention to perform ‘Umrah before setting out on his journey must enter iḥrām at the mīqāt of his country through which he passes. Whoever fails to do so, passing beyond the mīqāt without entering iḥrām, and does not return, has sinned, and must repent to Allah, the Exalted; and he must offer a sacrifice, to be distributed among the poor of the Ḥaram. And Allah, the Exalted, knows best.
Is it permissible for a woman to wear underwear while performing Umrah?
Yes, it is permissible for a woman to wear underwear while performing Umrah. This is because she should keep her regular clothes that cover all her body while being in a state of Ihram (ritual consecration) for Hajj, or Umrah. However, she should uncover her face and hands, but it is permissible for her to let her head-covering garment drape from her head down over her face when non-Mahram (i.e., marriageable) men pass by her. And Allah Knows Best.
Is it permissible for a woman to ride a taxi without a Mahram (unmarriageable kin) in order to attend a gathering of knowledge?
It is permissible for the woman to pursue the knowledge that she needs in order to perform the religious requirements due on her if there was nobody to teach her at home, provided that there is no temptation involved. Moreover, we don`t recommend that she rides a taxi without a Mahram although such an act isn`t from the forbidden Khulwah (seclusion).
A pious man proposed to me and my father was hesitant in this regard because he is black, am I sinful if I accepted his proposal?
If the suitor is pious, color isn`t a drawback. However, try talking to your father kindly, so that he approves of your marriage with contentment, and that is better for you.