en_tn_condensed/job/06/30.md

Is there evil on my tongue?

"I do not say wicked things." or "Do I say wicked things?"

on my tongue

"in my speech"

Cannot my mouth detect destructive things?

"I know what is right to say and what is wrong to say.". Job rebukes his friends and emphasizes that he can tell the difference between right and wrong. Job refers to himself by his "mouth" to emphasize his speech.