Grimrock

I know I can specify if a torch holder has a torch or not, but how can I find if the torch in the sconce has fuel? Would I have to do this individually for every possible torch that could go into a torch holder?

There is no way that I know of, other than to track it the entire time.

If the only way a torch can get into a torch holder is by the party putting it there, then you can run a repeating check whenever the player is standing in front of the torch holder and check the mouseItem if it is a torch and how much fuel it has, and if the mouseItem WAS a torch but is now empty then if the torch holder is suddenly full then that torch must have gone into the torch holder

Maybe you can use a custom alcove that looks like a sconce to accomplish whatever your in-game goal is?

Find the entity in the torch holder (e.g. using entitiesAt) and check for fuel using getFuel()?

that can work well if there is no torch on the ground there