If you want to find nth Salary from a table where n can be any number,
Query for finding the nth Salary:
SELECT DISTINCT Salary FROM tblemployees ORDER BY Salary DESC LIMIT 1 OFFSET (n-1)
If you want to find 5th highest salary, your query should look like :
SELECT DISTINCT Salary FROM tblemployees ORDER BY Salary DESC LIMIT 1 OFFSET 4
Note: OFFSET starts from 0th position, and hence use N-1 rule here