10.The King asked, “Whether advocates had liberty to plead in causes manifestly known to be unjust , vexations or oppressive?” Explain this in your own words.

The political situation was not so corrupted in Brobdingnag. The constitution was simple and just. The king did not understand what is meant by "Secrets of state" , mentioned by Gulliver. If a court case was clear it was not tampered by the Brobdingnagians further. So the King asked "wether the advocates had the liberty to plead(defend, in this case) the cases which are explicitly unjust?", i.e. in which the victim and victimizer are clear. 
This question is actually asked by Swift. It is a loophole in the clever structure of English Judiciary. The Brobdingnagian King is only his mouthpiece.