As far as I know, there is a master toggle to set all reactions to the "always ask" function.
It is not located in settings, but rather the "difficulty" tab. If you go to the difficulty settings, one of the options is "always ask reactions" or something of the sort, can't recall the exact verbage off the top of my head, but it is something similar to that.
That being said, this is a very nonsensical place to include it, as it makes much more sense for it to be included in the settings menu, where all the other game settings are kept.
Tying it to difficulty needlessly locks honor mode players out of the usability of this function and creates confusion as to this setting's existence.
Note: Toggling this setting to "always ask" also does not change the setting to opportunity attacks on all player characters and companions, as these will still automatically trigger without the pop up window and must still be manually changed to "always ask". This is another problem with this function.