Better Modifer to Denote Knowing What Something is Than, "...I know what it is?"

In Portal, GLaDOS says, "You are kidding me. Did you just stuff that aperture Science thing we don't know what it does into an Aperture Science emergency incinerator? That has got to be the dumbest thing that- woah wOah WoAH~" and something about that full sentence, "we don't know what it does" used as an adjunct really bothers me. People do this a lot too. Removing 'is' might make it a little better, but I'm pretty sure that still wouldn't be correct. In that particular case, she could have said, "...thing whose function we don't know..." (Although something shorter and without the inanimate 'whose' would be nice) but I don't know what word one would use like that in place of 'purpose' for what something is. There are some that kinda work, but they're all a little too specific: type, variety, specification, and classification all imply a set of possibilities, into one of which our thing fits, identity is mostly for people, and other words have other problems. (I did do some thesaurus and dictionary seeking.)

Do y'all have a better phrase than, "whose ___ we don't know," or a better word than the ones I listed? Thanks.

You say "used as an adjunct" but I think it is really "used as a modifier". "Whose function we don't know" does just that: it modifies, or more precisely it determines the preceding noun phrase (there is no comma); if there were a comma it would merely describe (describe further, and in doing so, still modify). Something short is possible in the way of a prepositional phrase: "of no known purpose to us".

• "You are kidding me. Did you just stuff that aperture Science thing of no known purpose to us into an Aperture Science emergency incinerator?"

Otherwise, if the context (more current, I would say) is such that "of no known purpose to us" carries a connotation of overspecification, a connotation that can already be suspected in the awkward formulation (the form of the modification or its syntaxical correctness has little to do with this semantic effect) a yet shorter form can be used: "of no known purpose".

• "You are kidding me. Did you just stuff that aperture Science thing of no known purpose into an Aperture Science emergency incinerator?"