If it is on a unique layer...no need to know what layer it is on, just freeze it and move on...
If it isn't then, one would need to edit the style...or while in there, just create the DREF and switch to that and not use the xref...
I don't see how knowing what layer it is on helps...IF it isn't on a unique layer from other objects you still can't freeze or turn it off without ill effects.
"Hey look it's on Layer ZERO and so is everything else....!"