how to use substring with a delimiter
you can use instr function to get the position of last /
-1 = you are looking from the end of the string
than you add 1, so you start position will be the first number after /
you do not need the third parameter in substr if you need substring till the end of a string

select substr(Emp_Num_ID,instr(Emp_Num_ID,'/',-1)+1) as Emp_ID from Employee_M