"Order By" Clause needn't be added to the end.

I got same result set with and without Order Clause.

Really we needn't use "Order By" Clause again.

Because

1) default order of row_number() window function is in ascending order.

2) default order of partition by emp_no is in ascending order.

3) we also used salary in ascending order in second row_number() function.

This is My answer for Q1. I used subquery that is used just for filtering to know that this employee is manager or not.

select emp_no,salary,row_number() over () as 'Row_Number1',
row_number() over (partition by emp_no order by salary) as 'Row_Number2'
from salaries 
where emp_no in (select emp_no from dept_manager);