Is knob and tube wire considered copper-clad-aluminum?
That old wire is tinned- they did that a long time ago for protection against the corrosive properties of the old rubber insulation, iirc.
Scrape some of tinning and you will see copper. The dead giveaway for tinned vs copper clad is the insulation type of the wire: If rw or rubber like in texture or "feel" it's going to be tinned copper almost certainly- by the time cc al hit the scene rw had been replaced by tw.
To further complicate stuff, I believe that tinned nm with tw insulation was made briefly same as cc al nm . To tell the difference maybe just look at the jacket- if its braided clothy tarry stuff, its most likely tinned copper. If its a slick plastic jacket, probably cc al, as most braided jackets were gone too, afaik, by the time cc al nm came out in late 60's- early-'70s. CC al is also not the silver color of tinned k&t.