Jonathan finished the extraction of the essence stone. He didn't bother to extract any skill from the taskforce because he didn't see any worth one when he was fighting them.
The martial artist ability users in the taskforce were all having E ranked skill. Only one of them had a D ranked skill and Jonathan didn't see it valuable enough to extracted.
He debated on it for a few seconds before Jonathan decided to extract the skill.
[Skill has been extracted.
D ranked skill— Combo Attack.]
He decided to extract the skill because he discovered that the skill might be a tricky one. He didn't give the Martial artist to perform the skill earlier, so he didn't how deadly the skill was, and meanwhile, it could be useful in his hands.