"But most of all, my brothers and sisters, never take an oath."
The rules in North Dakota and America generally allow you to sincerely affirm rather than solemnly swear, and you don't have to put your hand on a Bible or end with the God part; but I would probably get into at least temporary trouble on the rest of the oath.
First off, I'd be really, really tempted to recycle the old joke, "Hey, if I knew 'the truth, the whole truth, and nothing but the truth' I'd be God." A joke, even an insightful one, would probably be a bad idea: agents of the US criminal justice system routinely handcuff people just accused of crimes or make anyone they feel even slightly threatening get down on their knees or get "nose and toes" on the ground, so we're talking serious control freaks who probably aren't much into law jokes or any other kind of humor.
I might try, "I promise to answer the questions put to me truthfully, as well as I can and as completely as I may." If the judge demanded an explanation for my not just responding to the oath question with "Yes" or "I do," I might try, "Well, the oath you want me to take made some sense back when witnesses were just ordered to tell their stories, but nowadays a witness is supposed to respond to questions, and even the best answers to bad questions might not help reveal the truth — and as far as the whole truth goes, that could require more time than a trial allows. I really do try to be honest, and I don't want to swear to do something I could go to jail for trying to do." As in responding to a question with something like, "Look, counselor, that question isn't going to get us anywhere; what happened was —" And then I'd probably be offered the choice of answering the question or contemplate the majesty of the law while locked in a cell. Ditto if I tried to answer at sufficient length to get to "the whole truth."
For me, anyway, a student of language (well, and a curmudgeonly smart-ass), there's an irony here: People casual about words and about speaking truly can take the witness oath without qualms; those who take words, and their word, seriously might find themselves in trouble with the law.