Should the father command his ten-year-old daughter to wear the Islamic dress?

All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upon all of his family and companions.

The father should order his daughter to put on the Islamic dress once she turns ten, in order for her to get used to it. 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).

Is it permissible to delay menses by using medication in order to fast Ramadhaan?

It is permissible for a woman to use medication in order to delay her menses so that it becomes lawful for her to fast Ramadhaan, but it is better that she doesn`t do so, and taking the medication is prohibited if she, or her doctors know that it involves a risk on her health. And Allah Knows Best.

Is Zakah (obligatory charity) due on land intended for selling?

Yes, lands intended for selling are evaluated, 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.