To get the day of the week you can use
To_Char(MyDateColumn,'D')
.
It will give you a number from 1 to 7 where 1 is Monday and 7 is Sunday.
So if you run
Select *
FROM MyTable
WHERE To_Char(MyDateColumn,'D') != 7
You will have excluded Sundays from your query.
Just keep in mind that using functions in the WHERE clause is bad for performance. So it would be preferred if you can use the function in the SELECT clause instead.