Can anybody please direct me if AISC 9TH Edition, anywhere has stated about max. allowable beam cope size?
Or any other code or refrences that suggested anything.
I'm not aware of any. It's all governed by block shear failure. In bridge work for NYSDOT copes with a radius greater than 6" require longitudinal stiffeners.
I know of no code limitation on code size. However, a large cope usually implies a reduced connection length along the web. If your connection length is less than about 0.6h, you might start to consider whether or not the end of your beam is torsionally braced.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.