The son of one of the most iconic figures in country music, Lukas Nelson faces a colossal challenge as he attempts to establish an individual identity. His mission is complicated by a pinched voice that's almost indistinguishable from the one associated with hits like "Whiskey River" and "On the Road Again." Yet Thursday at Knuckleheads, Nelson proved to an audience of about 350 that he's well on his way to becoming his own man