What is the ruling regarding a man divorcing his wife by saying: "Divorce on you, from whom no one knows," while he is under duress from a threat? Is this considered an oath or a divorce? And what are the implications in both cases?

Paying a bribe is forbidden, except if it is the only means to obtain a right that cannot be acquired otherwise. In such a case, the sin falls upon the recipient of the bribe. Your statement, "a divorce from my wife no one knows about," is an indirect form of a conditional divorce. If you intended to condition your wife's divorce on informing someone about the bribe, and then you informed your colleagues, divorce has occurred according to the majority of scholars. What you mentioned about work suspension is not considered duress that prevents divorce. You can take your wife back if this divorce does not complete the three divorces. However, if you did not intend divorce by what you uttered, then nothing is binding upon you.