I think pretty much all the cats mentioned in Harry Potter are Kneazles. Crookshanks is part kneazle, and all of arabella figg's cats are kneazle and so is filch's cat, mrs norris, which is why she's so creepy and hangs around all the time.
they look like cats and are very intelligent, independent and occasionally aggressive, and have an uncanny ability to detect suspicious and distrustful people. (for example when crookshanks kept attacking scabbers, aka pettigrew.)
i remember jkr saying that but i dont think its actually that important, just a fun fact. you could read fantastic beasts and where to find them for more info.
(just remembered, in deathly hallows, the letter harry found from lily to sirius mentioned baby harry almost killing the cat with his toy broomstick, maybe it was a kneazle? i also seem to remember someone telling me that that cat might be crookshanks which is why he likes harry or something..? :S)
hope this helps!
X