Dear Ahmed,
Create an derivation rule Enhancement type and use SY-DATUM to get the current date.
You can use FM DATE_COMPUTE_DAY to get the day of the week based on this date.
The return is:
1 - Monday
2 - Tuesday
3 - Wednesday
4 - Thursday
5 - Friday
6 - Saturday
7 - Sunday
I hope it helps you.
Best regards,
Gabriel Coleti