1/4 cup of whiskey in cupcake batter substitute what type of liquid? And use the same amount?
The whiskey is there to add flavor. If it were in the praline centers it might have some texture effect too, but in the batter, especially in this small an amount, it's really only going to matter for flavor.

You should be able to substitute water, plus an appropriate amount of some kind of flavored extract you do want - vanilla, rum, or anything that sounds good to you. (If alcohol is a problem I guess you'll need an alcohol-free one.) You could also simply find another recipe that doesn't use it.

That said, if it's just that you don't want to buy a whole bottle of whiskey, you can likely get a tiny bottle to use just for this recipe, and not have a ton left over. If you suspect you wouldn't like the flavor, do keep in mind that a quarter cup of whiskey is a pretty small amount of alcohol when spread across a whole batch of cupcakes, so it could be worth giving it a try. But if you really just don't want to consume any alcohol, water should be fine.