Thanks. Su-37 corrected to single-seater.
All I know about the Su-30KN is that it's an Navy flanker with updated avionics. Prototype bort #302 was shown at the 2000 Gelendzhik
Hydroaviasalon. In 2000/2001 timeframe they were planning to build around 30 Su-30KNs, though I don't know if that is still accurate.
It's a 2-seater based on the Su-30/Su-27UB/Su-27UBM lineage, with enlarged tail stinger for fuel. The 30KN has upgraded multifunctional avionics,
compared to the navalized Su-27K/Su-33.
Airwar.ru article on Su-27UBM
Su-30MK2 might be shorthand for the MKK.