From Rap Dictionary
KJ-52 is rapper Jonah Sorrentino. The nickname is, as the title track of his 2003 release explains, pronounced "five-two." "KJ" derives from an older nickname (apparently "King J Mack"). The "52" refers to the five loaves and two fish Jesus used to feed 5000 (Matthew 14:13-21), alluding to how KJ has given his talents (which he deprecates) over to Christ, who has used them to feed people spiritually.