Dak will tell Mither about the victory, and how he led the army to a great success... and he will throw in that Wraith and Ker were a key part of that success. Without them, we might have fallen, but with them our victory was assured.
He will tell the Great Leader that a matter concerning the Force and Jedi ways has come up, and he needs to interrogate the prison about them. If Mither insists on being there, then as much as he regrets it, Dak thinks Gremon will be more forthcoming without the Great Leader's presence.
Mither can be found in the small cavern where he has squirreled away his belongings and comfortable seats that don't irritate his dry and flaky scales.
"I do not care about the Outsssidersss partsss in thissssssss," Mither hisses harshly when you tell him. "But Meja'Tsssid is oursss. Well done, General. I am MOST pleasssed."
When you bring up the Jedi ways, Mither flicks his tongue nervously.
"What could you posssssibly want to know from the lying Prince?"