1. Is it permissible to do Nikah when the bride and bridegroom do not know each other? 2. Does the girl's consent in absence validate the Nikah conducted by the parents of two sides with the presence of the boy?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

It is permissible for a Muslim man who wants to marry to look for a religious girl as instructed by the Prophet Muhammad who said: “A woman is married for four things: for her wealth, her family lineage, her beauty and her religion. So choose the religious one, you will prosper.” [Al-Bukhari and Muslim]

Similarly, it is permissible for a Muslim woman to marry a religious Muslim man as the Prophet said: “If a man whose religion and moral conduct are pleasing to you proposes to you, then let him marry; otherwise there will be great mischief and corruption on earth.” [Ahmad]

Knowing a person, his/her character, personality and religiousness is possible by asking those who know him/her.

However, Islam does not allow, before marriage, personal relationships or dating since most of the time that leads to some prohibitions, like being alone with each other, looking with sexual desires, etc. 

Besides, a girl's consent is enough for a valid marriage; her presence at the marriage contract is not compulsory.

Allaah Knows best.