Job appeals to his friends to give him a fair hearing. Let them look him in the face (Job 6:28). We must imagine, says Duhm, that during Job's speech, and especially during the last sharp sayings, they have exhibited their disapproval by turning away from him. Surely (Job 6:28) is the formula of oath literally, if I shall lie to your face (then may evil befall me) (cf. Job 1:11).
Job 6:29 means Turn to me and hear me: it is not injustice to complain as I do.
Job 6:30 means Cannot I correctly discern the nature of my calamity (and perceive its injustice)? The first clause means the same as the second has my tongue become perverted so that it cannot tell good from bad?