This week, at least, Donald Trump's boast that ''The Apprentice'' is the top show on TV is correct. According to Nielsen, some 27.6 million people tuned in to NBC to watch Thursday night's series finale, in which the Donald finally made his hiring decision and picked Bill Rancic over Kwame Jackson. TV's usual number one show, CBS' timeslot competitior ''CSI: Crime Scene Investigation,'' drew 23.6 million, or about 2.5 million fewer than usual. The ''Apprentice'' audience was NBC's biggest for a non-Olympic event on a ''must-see Thursday'' night in at least three years and its biggest audience of 18-to-49-year-olds in any timeslot since Oct. 2002. Meanwhile, with no more Trump theatrics until fall, we're ready for ''Average Apprentice: Kwame Returns.''