ਮੈਂ ਇਹ ਜਾਣਨਾ ਚਾਹਾਂਗਾ ਕਿ ਹੁਕਮਨਾਮਾ ਕਿਵੇਂ ਅਤੇ ਕਦੋਂ ਅਰੰਭ ਹੋਇਆ ਅਤੇ ਅਸੀਂ ਇਸਨੂੰ ਕਿਉਂ ਲੈਂਦੇ ਹਾਂ।

Respected Veer Kuldeep Singh Jio;

Thanks for asking this question;
It very important to understand the reason behind some of the ritualistic practices in Sikhi.

I am unable to find any reference to Hukam Nama and its process in Guru Granth Sahib Gurbani.

It could have started with the very first Parkash of BEERH SAHIB, the name used to refer to the Granth Sahib at that time.
However, regardless of when it started, the purpose appears to be staying connected with Gurbani and making learning from it an all-time habit. Every morning, evening ,and whenever one initiates any tasks/projects etc.

The specific practice of taking Hukam Nama, reading the SABD that appears on top the left page, and going a page back in case it starts at previous page, is specifically defined by Rahat Maryada in later times (1925 to 1945).

It appears to be a practice started as way of learning from Gurbani, seem to have turned into a ritual and assumed that this particular SABD has specific meaning for that day, and including that the Hukam Nama from one place, e.g., Darbar Sahib Amritsar, is somehow more important than one at your local Gurduara Sahib, or at your own home, is additional superstition and is inconsistent with Gurbani message.