Up On Meaning

(idiomatic) Well-informed concerning.

Example:   The tour guide was certainly up on his history.
2001 June 24, Christopher John Farley, "The New Video Wizards," Time:
  Says Sigismondi: "I don't watch [MTV]. I'm really not up on what's trendy."
2011 Aug. 25, William Grimes, "Casey Ribicoff, Senator’s Widow and a Style Leader, Dies at 88," New York Times (retrieved 3 Jan 2012):
  â€œShe was up on everything,” said the biographer A. Scott Berg. “Not just the news but every play or film or book.”