What is Salat E Hajjat Namaz and How to Perform It. Also tell me which dua should be recited?

Salatul Hajat is simply 2 rakat of Nafil Namaz and nothing else no special Dua no special Surah.

After praying 2 rakat Nafil Sit Calmly recite Darood e Ibrahim, and ask Allah Whatever you want following Asma e Azam and then at the end of Dua repeat Darood e Ibrahim. Khalas.

2nd Option Recite Darood e Ibrahim Continue as Prophet صلى الله عليه وسلم States in 1 Hadith (Mafhoom of Hadith i am writing here)

If you recite Darood e Ibrahim in whole time of your Dua Then surely Allah will take care of your problems.

Recite Sayyed ul Isteghfar or Simply Astaghfarullah….

Because Allah says in Surah Nuh 71 in between aayat Number 10–16, if you ask forgiveness I will forgive you and I will you give you gardens, Money, Childrens, Etc. (Mafhoom of Aayat)

Hope you will get what you want In'Sha Allah.