As your opponent's
Word of Command is resolving, you'll get to decide what decisions your opponent makes about what decisions you make. As whatever you forced your opponent to force you to cast is resolving, your opponent gets to decide what decisions you make.
But in order for any of that to occur, you first have to resolve a Word of Command against an opponent who has a Word of Command in their hand and the mana to cast it but who for some reason doesn't respond to your Word of Command by either casting theirs or rendering themselves unable to cast it. And that's going to be a neat trick. Let me know if it ever happens for real; I'd like to see it.
In future, these kinds of artificially constructed corner-case scenarios would likely be better asked in the Wizards Community's
Rules Theory and Templating forum. There's very little practical value in answering them here, since not much can be learned from them that will be applicable to actual games of
Magic. But if you like coming up with weird theoreticals for the sake of it, you'll find a number of like-minded people in RT&T willing to hash them out with you. (And hey, at times I'm one of them.)