This isn't possible to do - you don't know in many cases if your opponent is holding an item (in Gen 8/9, whether or not a Pokemon is holding an item is not revealed at Team Preview) nor if your opponent is holding an item that can't be removed (e.g. Z-moves in Gen 7 or Mega Stones attached to the appropriate Mega in 6/7). In general, tooltips only display information the player can know for sure. In fact the vast majority of the time, Knock Off will have 97 BP, because it will be removing items, but you can't know that in advance unless you've confirmed the opponent does have an item that can be removed via Knock Off, which is probably going to be after using Knock Off itself in the majority of cases.